Major dependency update (#1974)

* [V3] Stop `tmp` dir showing up

* [V3] Remove requirements.txt and declare in install_requires

* Remove requirements.txt from tox.ini

* Update and pin all dependencies and sub-dependencies

* Update for breaking changes

* Reformat

* Update docs/requirements.txt and tox.ini requirements

* Add 3.7 to identifiers and travis/tox builds

* Attempt at fixing the travis build matrix

* Attempt #2

* Attempt 3

* aiohttp.ClientSession.close() -> detach() in sync code

* Add raven-aiohttp to requirements

* Fix stuff in setup.py

 - Added discord.py back into requirements list
 - Fix typo in alabaster extra requirement

Also in the Pipfile:
 - Removed allow_prereleases and explicitly pinned black, since this is the only dep we want a prerelease for.

* Update to Rapptz/discord.py@8ccb98d395

* Add proper 3.7 build in Travis

See travis-ci/travis-ci#9815

* Which version of 3.6 does Xenial install then?

* Maybe we should stop pipenv installing useless stuff

* Nevermind, back to specific minor version

* Remove lots of WET dependency stuff

* Fix egg fragment for dependency link

tox.ini

@@ -6,24 +6,27 @@
 [tox]
 envlist =
     py36
+    py37
     docs
     style
 
 [testenv]
 description = Run unit tests with pytest
+whitelist_externals =
+    pytest
 extras = voice, test, mongo
 deps =
-    https://github.com/Rapptz/discord.py/archive/7eb918b19e3e60b56eb9039eb267f8f3477c5e17.zip#egg=discord.py[voice]
-    -rrequirements.txt
+    -r{toxinidir}/dependency_links.txt
 commands =
     python -m compileall ./redbot/cogs
     pytest
 
 [testenv:docs]
 description = Attempt to build docs with sphinx-build
-whitelist_externals = sphinx-build
+whitelist_externals =
+    sphinx-build
 basepython = python3.6
-extras = voice, docs, mongo
+extras = docs, mongo
 commands =
     sphinx-build -d "{toxworkdir}/docs_doctree" docs "{toxworkdir}/docs_out" -W -bhtml
     sphinx-build -d "{toxworkdir}/docs_doctree" docs "{toxworkdir}/docs_out" -W -blinkcheck