Prevent multiple tick conversions

Adds internal state and checks to Pattern and Track to prevent duplicate
calls to make_ticks_abs() and make_ticks_rel(). Fixes #20.
Merge pull request #34 from tdhsmith/master

Prevent multiple tick conversions
Functions get_pitch() and set_pitch() added to class AfterTouchEvent.
Merge pull request #45 from Erriez/master

New functions added to class AfterTouchEvent.
Added MetaEvent 0x08.
According to MIDI recommended practice 19, it is recommended to be used as "Program Name".
(http://www.midi.org/techspecs/rp19.php)
Merge pull request #46 from hskim08/master

Added MetaEvent 0x08.
Merge remote-tracking branch 'vishnubob/master'