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.