Merge branch 'release/0.1' into develop
Document things roughly.  Good enough.
Comment out the loop-reset notification.
Full(er) drumming deck.
Remove the reset looper thread.
And finish refactoring code ou.t
Tidy up the reset thread.
Add some melody
Bump version number and release notes.
Merge branch 'release/0.2'
Merge branch 'release/0.2' into develop
Bump version numbers.
Blargh can't spell.
Use our channel number to map into the SDL mixer.

This enables us to axe known channels in the future, and hopefully
doesn't cause too much breakage in the now.
Do channel halting on channel commence.
Move the mixer halting out of the SDL check.

This enables a 'stop-the-channel' behaviour a la Ableton, where it is
possible to stop any playing loop by tapping a blank square on that
column.
Refactor out the audio kill.
Oops, I broke SDL::Mixer.

SDL::Mixer, intuitively, calls one function `play_channel` and the
others `halt` or `pause`.  wat.
Blink the button if there's no audio.
Tidy up audio killing.