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

docs/requirements.txt

@@ -1,37 +0,0 @@
--i https://pypi.org/simple
-alabaster==0.7.10
-appdirs==1.4.3
-atomicwrites==1.1.5
-attrs==18.1.0
-babel==2.6.0
-black==18.6b2
-certifi==2018.4.16
-chardet==3.0.4
-click==6.7
-docutils==0.14
-idna==2.6
-imagesize==1.0.0
-jinja2==2.10
-markupsafe==1.0
-more-itertools==4.2.0
-packaging==17.1
-pluggy==0.6.0
-py==1.5.3
-pygments==2.2.0
-pyparsing==2.2.0
-pytest-asyncio==0.8.0
-pytest==3.6.1
-pytz==2018.4
-requests==2.18.4
-six==1.11.0
-snowballstemmer==1.2.1
-sphinx-rtd-theme==0.4.0
-sphinx==1.7.5
-sphinxcontrib-asyncio==0.2.0
-sphinxcontrib-websupport==1.1.0
-toml==0.9.4
-tox==3.0.0
-urllib3==1.22
-virtualenv==16.0.0
-yarl==0.18.0
-git+https://github.com/Rapptz/discord.py@7eb918b19e3e60b56eb9039eb267f8f3477c5e17#egg=discord.py-1.0