Added mkv_track_id to extracted subtitle to support multiple subtitles with the same language
Yield the current subtitle filename and time elapsed for better output control
Default audio channels to 2 if not available
Merge branch 'master' of github.com:gokuu/mkv

Conflicts:
	lib/mkv/movie.rb
Enable extracting subtitles in multiple languages in one go
Default track language information to english if not provided
Added track type methods
Added unit tests