Make AuditTrail use an ActiveRecord association to expose and build audit events
Fix Mongo backend to match new API.
Fix Travis CI config file.
Use bundler for gem management tasks.
Bump version.
Use https for rubygems in gemspec
Add license to Gemspec file
Bump version to 0.1.5
Merge remote-tracking branch 'upstream/master' into patch-1

Conflicts:
	lib/state_machine/audit_trail/backend/active_record.rb
	state_machine-audit_trail.gemspec