Added the release version

Fixed ImportError on py2.7 if trollius not installed

Fixes agronholm#403.

Updated version history and added the release version

Updated the changelog

Added the release version

Fixed class methods being mistaken for instance methods

Fixes agronholm#330.

Raise RuntimeError if starting the scheduler under uWSGI without threads

Compare next_date to start_date, not previous_fire_time

Bumped up the fallback version

Added Gitter webhook