Praw 19 November -- Early support for Multireddits

New :class:`Multireddit` for multireddit objects. Proper endpoints and kind added to init config

New :meth:`get_multireddit` to get a single mr object. Standard usage: `r.get_multireddit(multi_author, multi_name)`

New :meth:`get_my_multis` which requires logged in scope. Returns a list of all multireddit objects you own.

New :class:`MultiredditTest` in tests which will test the get_my_multis function. As of writing, :class:`BasicTest` will test get_multireddit since that does not require logged in.

Added proper material to CHANGES.rst

Edit: Travis build failed but I see the error and will re-commit.

Sorry for the commit-flood :( I will learn to squash before next time.

Edit: [Build 498 failed on account of test_scope_submit timing out](https://travis-ci.org/praw-dev/praw/jobs/41518483#L415) (Line 415). Can a new build be initiated without a commit?
"Return a list of all the Multireddits for the authenticated Redditor."