Wunderpy

Fix python 3 support.

Another bugfix.

Bugfixes

Client
- Add TaskList and Task classes
- Add filtering methods
- Add tests for new classes and most Wunderlist functionality

CLI
- Add --today and --week options
- Only display incomplete tasks by default, add --show-complete option.

- Add a CLI interface
- Ensure session headers are included in all requests

Almost everything has been revamped, and most of the code is now covered by unit tests.