Added commands to login, show liked mixes,(un)like mix,(un)favorite track.

Changes in api.py:
Add obtain_user_token and post to log in to 8tracks.
Add get_mix_liked was added to show liked mixes by current user.
Add like_mix, unlike_mix, fav_track and unfav_track.

Changes in client.py:
Add login commands.
Added autologin function using config info in preloop (not sure if it's the right place to do so).
Added liked commands.
Added like_mix, unlike_mix, fav_track and unfav_track and aliases.
Added get_logged to check if user is logged in.

Changes in README.rst:
Added descriptions for new commands.
PEP8 guidelines fixes.
Add autologin command and miscellaneous fixes.

Changes in api.py:
- payload variable is splitted in two variable (username and password) in _obtain_user_token method.
- username is now stored as self._user_name in _obtain_user_token method.
- get_mix_liked method renamed as get_liked_mixes.
- self.user_token marked as private.
- Modify get_liked_mixes docs.

Changes in client.py:
- Add do_autologin method to toggle autologin on|off.
- Refactored autologin in preloop to use do_login method.
- Fix do_login to allow password with spaces.
- Add ConnectionError exception to do_login method.
- Renamed get_logged method as get_login_status.
- Renamed self.logged variable as self._logged_in.
- Renamed do_like method as do_liked_mixes.

Changes in README.rst:
- Modified command name subsquently to method renaming.
- Added autologin command description.
Fix autologin method : credentials can now be saved at any time.
Merge pull request #31 from octogene/master

Add login and other commands.