Require Mopidy >= 0.18
Remove dependency check done by Mopidy
Use new extension setup() API
Replace discontinued crate.io with PyPI links
Let setup.py control the version of gmusicapi that is installed
Use new backend API locations
Fix tests
Ensure all files are packaged on PyPI
Use loggers namespaced to mopidy_gmusic.*
Merge pull request #22 from jodal/mopidy-0.18-updates

Mopidy 0.18 updates