WIP: 3.0.0

## 3.0.0

- Changed ``twython/twython.py`` to ``twython/api.py`` in attempt to
make structure look a little neater
- Removed all camelCase function access (anything like
``getHomeTimeline`` is now ``get_home_timeline``) Fixes #199
- Removed ``shorten_url``. With the ``requests`` library, shortening a
URL on your own is simple enough
- ``twitter_token``, ``twitter_secret`` and ``callback_url`` are no
longer passed to ``Twython.__init__`` Fixes #185
    - ``twitter_token`` and ``twitter_secret`` have been replaced with
``app_key`` and ``app_secret`` respectively
    - ``callback_url`` is now passed through
``Twython.get_authentication_tokens``

[ci skip]