Things to do:

 - Implement parsing of sysexes chopped into several "packets".

 - Add support for type 2 SMF files.

 - Add support for SMPTE time.

 - Rework removal of tempo changes.  Right now there is one scenario that is broken - when
   you have two tempo-related events at the end of the song (i.e. there are no events following),
   removing one of these tempo-related events will remove both tempo changes.

 - Add a way to force some particular tempo during playback and ignore the following tempo changes.

