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

redbot/pytest/core.py

@@ -178,7 +178,7 @@ def red(config_fr):
 
     yield red
 
-    red.http._session.close()
+    red.http._session.detach()
 
 
 # endregion