Add documentation lookup support. (#53)

* Allow users to query documentation link.

* Show symbol signature and excerpt from docs.

* Use `•` character for showing list items.

* Trim whitespace after two newlines.

* Allow users to query documentation link.

* Show symbol signature and excerpt from docs.

* Use `•` character for showing list items.

* Trim whitespace after two newlines.

* Add docstrings, simplify command.

* Use a cache for getting doc embeds.

* Suppress `urllib3` log messages below WARNING.

* Use shared `http_session` on the bot.

* Comment `fetch_initial_inventory_data`, unpack URL directly.

* Address various review comments.

- use `str.format` for generating the stdlib documentation URLs
- move `convert_code` comment to a docstring
- fix up python syntax parsing by not using a `*`
- send red error embeds when documentation could not be found

* Use `lxml` for HTML parsing.

* Pin yarl to 1.1.1

* Use the website's API as package documentation metadata database.

* Fetch inventories concurrently.

* Use red error embed & error title on error.

* Add examples to command docstrings.

* Use typing notifications instead of edits.

* Flush cache on inventory refresh.

* Address @martmists' review comments.

* Use `BadArgument` instead of custom exception class.

* Move universal converters to `bot/converters.py`.

1 files changed, 154 insertions, 2 deletions

diff --git a/Pipfile.lock b/Pipfile.lock
index 64652ae3b..9f4c3a1d4 100644
--- a/Pipfile.lock
+++ b/Pipfile.lock
@@ -1,7 +1,7 @@
 {
     "_meta": {
         "hash": {
-            "sha256": "1529809913b543e7fbbf6091c33369f96567ab1fc8d7d637df574d4ac9d8b050"
+            "sha256": "2475ab039e5ce97636b9a255dd7e21b67e7b66d832f341b4065876f7535b2d88"
         },
         "pipfile-spec": 6,
         "requires": {
@@ -51,6 +51,13 @@
             "index": "pypi",
             "version": "==2.2.5"
         },
+        "alabaster": {
+            "hashes": [
+                "sha256:2eef172f44e8d301d25aff8068fddd65f767a3f04b5f15b0f4922f113aa1c732",
+                "sha256:37cdcb9e9954ed60912ebc1ca12a9d12178c26637abdf124e3cde2341c257fe0"
+            ],
+            "version": "==0.7.10"
+        },
         "async-timeout": {
             "hashes": [
                 "sha256:474d4bc64cee20603e225eb1ece15e248962958b45a3648a9f5cc29e827a610c",
@@ -58,6 +65,21 @@
             ],
             "version": "==3.0.0"
         },
+        "babel": {
+            "hashes": [
+                "sha256:6778d85147d5d85345c14a26aada5e478ab04e39b078b0745ee6870c2b5cf669",
+                "sha256:8cba50f48c529ca3fa18cf81fa9403be176d374ac4d60738b839122dfaaa3d23"
+            ],
+            "version": "==2.6.0"
+        },
+        "beautifulsoup4": {
+            "hashes": [
+                "sha256:11a9a27b7d3bddc6d86f59fb76afb70e921a25ac2d6cc55b40d072bd68435a76",
+                "sha256:7015e76bf32f1f574636c4288399a6de66ce08fb7b2457f628a8d70c0fbabb11",
+                "sha256:808b6ac932dccb0a4126558f7dfdcf41710dd44a4ef497a0bb59a77f9f078e89"
+            ],
+            "version": "==4.6.0"
+        },
         "certifi": {
             "hashes": [
                 "sha256:13e698f54293db9f89122b0581843a782ad0934a4fe0172d2a980ba77fc61bb7",
@@ -76,6 +98,14 @@
             "egg": "discord.py[voice]",
             "file": "https://github.com/Rapptz/discord.py/archive/rewrite.zip"
         },
+        "docutils": {
+            "hashes": [
+                "sha256:02aec4bd92ab067f6ff27a38a38a41173bf01bed8f89157768c1573f53e474a6",
+                "sha256:51e64ef2ebfb29cae1faa133b3710143496eca21c530f3f71424d77687764274",
+                "sha256:7a4bd47eaf6596e1295ecb11361139febe29b084a87bf005bf899f9a42edc3c6"
+            ],
+            "version": "==0.14"
+        },
         "dulwich": {
             "hashes": [
                 "sha256:c51e10c260543240e0806052af046e1a78b98cbe1ac1ef3880a78d2269e09da4"
@@ -98,6 +128,20 @@
             ],
             "version": "==2.6"
         },
+        "imagesize": {
+            "hashes": [
+                "sha256:3620cc0cadba3f7475f9940d22431fc4d407269f1be59ec9b8edcca26440cf18",
+                "sha256:5b326e4678b6925158ccc66a9fa3122b6106d7c876ee32d7de6ce59385b96315"
+            ],
+            "version": "==1.0.0"
+        },
+        "jinja2": {
+            "hashes": [
+                "sha256:74c935a1b8bb9a3947c50a54766a969d4846290e1e788ea44c1392163723c3bd",
+                "sha256:f84be1bb0040caca4cea721fcbbbbd61f9be9464ca236387158b0feea01914a4"
+            ],
+            "version": "==2.10"
+        },
         "logmatic-python": {
             "hashes": [
                 "sha256:0c15ac9f5faa6a60059b28910db642c3dc7722948c3cc940923f8c9039604342"
@@ -105,6 +149,53 @@
             "index": "pypi",
             "version": "==0.1.7"
         },
+        "lxml": {
+            "hashes": [
+                "sha256:01c45df6d90497c20aa2a07789a41941f9a1029faa30bf725fc7f6d515b1afe9",
+                "sha256:0c9fef4f8d444e337df96c54544aeb85b7215b2ed7483bb6c35de97ac99f1bcd",
+                "sha256:0e3cd94c95d30ba9ca3cff40e9b2a14e1a10a4fd8131105b86c6b61648f57e4b",
+                "sha256:0e7996e9b46b4d8b4ac1c329a00e2d10edcd8380b95d2a676fccabf4c1dd0512",
+                "sha256:1858b1933d483ec5727549d3fe166eeb54229fbd6a9d3d7ea26d2c8a28048058",
+                "sha256:1b164bba1320b14905dcff77da10d5ce9c411ac4acc4fb4ed9a2a4d10fae38c9",
+                "sha256:1b46f37927fa6cd1f3fe34b54f1a23bd5bea1d905657289e08e1297069a1a597",
+                "sha256:231047b05907315ae9a9b6925751f9fd2c479cf7b100fff62485a25e382ca0d4",
+                "sha256:28f0c6652c1b130f1e576b60532f84b19379485eb8da6185c29bd8c9c9bc97bf",
+                "sha256:34d49d0f72dd82b9530322c48b70ac78cca0911275da741c3b1d2f3603c5f295",
+                "sha256:3682a17fbf72d56d7e46db2e80ca23850b79c28cfe75dcd9b82f58808f730909",
+                "sha256:3cf2830b9a6ad7f6e965fa53a768d4d2372a7856f20ffa6ce43d2fe9c0d34b19",
+                "sha256:5b653c9379ce29ce271fbe1010c5396670f018e78b643e21beefbb3dc6d291de",
+                "sha256:65a272821d5d8194358d6b46f3ca727fa56a6b63981606eac737c86d27309cdd",
+                "sha256:691f2cd97cf026c611df1ea5055755eec7f878f2d4f4330dc8686583de6fc5fd",
+                "sha256:6b6379495d3baacf7ed755ac68547c8dff6ce5d37bf370f0b7678888dc1283f9",
+                "sha256:75322a531504d4f383264391d89993a42e286da8821ddc5ac315e57305cb84f0",
+                "sha256:7f457cbda964257f443bac861d3a36732dcba8183149e7818ee2fb7c86901b94",
+                "sha256:7ff1fc76d8804e0f870c343a72007ff587090c218b0f92d8ee784ac2b6eaf5b9",
+                "sha256:8523fbde9c2216f3f2b950cb01ebe52e785eaa8a07ffeb456dd3576ca1b4fb9b",
+                "sha256:8f37627f16e026523fca326f1b5c9a43534862fede6c3e99c2ba6a776d75c1ab",
+                "sha256:a7182ea298cc3555ea56ffbb0748fe0d5e0d81451e2bc16d7f4645cd01b1ca70",
+                "sha256:abbd2fb4a5a04c11b5e04eb146659a0cf67bb237dd3d7ca3b9994d3a9f826e55",
+                "sha256:accc9f6b77bed0a6f267b4fae120f6008a951193d548cdbe9b61fc98a08b1cf8",
+                "sha256:bd88c8ce0d1504fdfd96a35911dd4f3edfb2e560d7cfdb5a3d09aa571ae5fbae",
+                "sha256:c557ad647facb3c0027a9d0af58853f905e85a0a2f04dcb73f8e665272fcdc3a",
+                "sha256:defabb7fbb99f9f7b3e0b24b286a46855caef4776495211b066e9e6592d12b04",
+                "sha256:e2629cdbcad82b83922a3488937632a4983ecc0fed3e5cfbf430d069382eeb9b"
+            ],
+            "index": "pypi",
+            "version": "==4.2.1"
+        },
+        "markdownify": {
+            "hashes": [
+                "sha256:28ce67d1888e4908faaab7b04d2193cda70ea4f902f156a21d0aaea55e63e0a1"
+            ],
+            "index": "pypi",
+            "version": "==0.4.1"
+        },
+        "markupsafe": {
+            "hashes": [
+                "sha256:a6be69091dac236ea9c6bc7d012beab42010fa914c459791d627dad4910eb665"
+            ],
+            "version": "==1.0"
+        },
         "mpmath": {
             "hashes": [
                 "sha256:04d14803b6875fe6d69e6dccea87d5ae5599802e4b1df7997bddd2024001050c"
@@ -130,6 +221,13 @@
             "index": "pypi",
             "version": "==4.3.1"
         },
+        "packaging": {
+            "hashes": [
+                "sha256:e9215d2d2535d3ae866c3d6efc77d5b24a0192cce0ff20e42896cc0664f889c0",
+                "sha256:f019b770dd64e585a99714f1fd5e01c7a8f11b45635aa953fd41c689a657375b"
+            ],
+            "version": "==17.1"
+        },
         "pika": {
             "hashes": [
                 "sha256:63131aaeec48a6c8f1db1fe657e1e74cf384c3927eb7d1725e31edae4220dea4",
@@ -212,6 +310,25 @@
             ],
             "version": "==2.3.0"
         },
+        "pygments": {
+            "hashes": [
+                "sha256:78f3f434bcc5d6ee09020f92ba487f95ba50f1e3ef83ae96b9d5ffa1bab25c5d",
+                "sha256:dbae1046def0efb574852fab9e90209b23f556367b5a320c0bcb871c77c3e8cc"
+            ],
+            "version": "==2.2.0"
+        },
+        "pyparsing": {
+            "hashes": [
+                "sha256:0832bcf47acd283788593e7a0f542407bd9550a55a8a8435214a1960e04bcb04",
+                "sha256:281683241b25fe9b80ec9d66017485f6deff1af5cde372469134b56ca8447a07",
+                "sha256:8f1e18d3fd36c6795bb7e02a39fd05c611ffc2596c1e0d995d34d67630426c18",
+                "sha256:9e8143a3e15c13713506886badd96ca4b579a87fbdf49e550dbfc057d6cb218e",
+                "sha256:b8b3117ed9bdf45e14dcc89345ce638ec7e0e29b2b579fa1ecf32ce45ebac8a5",
+                "sha256:e4d45427c6e20a59bf4f88c639dcc03ce30d193112047f94012102f235853a58",
+                "sha256:fee43f17a9c4087e7ed1605bd6df994c6173c1e977d7ade7b651292fab2bd010"
+            ],
+            "version": "==2.2.0"
+        },
         "python-dateutil": {
             "hashes": [
                 "sha256:1adb80e7a782c12e52ef9a8182bebeb73f1d7e24e374397af06fb4956c8dc5c0",
@@ -234,6 +351,13 @@
             "index": "pypi",
             "version": "==0.12.0"
         },
+        "pytz": {
+            "hashes": [
+                "sha256:65ae0c8101309c45772196b21b74c46b2e5d11b6275c45d251b150d5da334555",
+                "sha256:c06425302f2cf668f1bba7a0a03f3c1d34d4ebeef2c72003da308b3947c7f749"
+            ],
+            "version": "==2018.4"
+        },
         "pyyaml": {
             "hashes": [
                 "sha256:0c507b7f74b3d2dd4d1322ec8a94794927305ab4cebbe89cc47fe5e81541e6e8",
@@ -254,6 +378,13 @@
             "index": "pypi",
             "version": "==3.12"
         },
+        "requests": {
+            "hashes": [
+                "sha256:6a1b267aa90cac58ac3a765d067950e7dbbf75b1da07e895d1f594193a40a38b",
+                "sha256:9c443e7324ba5b85070c4a818ade28bfabedf16ea10206da1132edaa6dda237e"
+            ],
+            "version": "==2.18.4"
+        },
         "shortuuid": {
             "hashes": [
                 "sha256:d08fd398f40f8baf87e15eef8355e92fa541bca4eb8465fefab7ee22f92711b9"
@@ -267,6 +398,28 @@
             ],
             "version": "==1.11.0"
         },
+        "snowballstemmer": {
+            "hashes": [
+                "sha256:919f26a68b2c17a7634da993d91339e288964f93c274f1343e3bbbe2096e1128",
+                "sha256:9f3bcd3c401c3e862ec0ebe6d2c069ebc012ce142cce209c098ccb5b09136e89"
+            ],
+            "version": "==1.2.1"
+        },
+        "sphinx": {
+            "hashes": [
+                "sha256:85f7e32c8ef07f4ba5aeca728e0f7717bef0789fba8458b8d9c5c294cad134f3",
+                "sha256:d45480a229edf70d84ca9fae3784162b1bc75ee47e480ffe04a4b7f21a95d76d"
+            ],
+            "index": "pypi",
+            "version": "==1.7.5"
+        },
+        "sphinxcontrib-websupport": {
+            "hashes": [
+                "sha256:7a85961326aa3a400cd4ad3c816d70ed6f7c740acd7ce5d78cd0a67825072eb9",
+                "sha256:f4932e95869599b89bf4f80fc3989132d83c9faa5bf633e7b5e0c25dffb75da2"
+            ],
+            "version": "==1.0.1"
+        },
         "sympy": {
             "hashes": [
                 "sha256:ac5b57691bc43919dcc21167660a57cc51797c28a4301a6144eff07b751216a4"
@@ -485,7 +638,6 @@
                 "sha256:6a1b267aa90cac58ac3a765d067950e7dbbf75b1da07e895d1f594193a40a38b",
                 "sha256:9c443e7324ba5b85070c4a818ade28bfabedf16ea10206da1132edaa6dda237e"
             ],
-            "index": "pypi",
             "version": "==2.18.4"
         },
         "safety": {