Load/save pattern data automatically (#16)
Also save BPM parameter (#16)
Fix segfault, save BPM as unsigned integer (#16)
Fix tap tempo BPM update bug
Print current BPM on screen
Use defined constant USECS_PER_SECOND to calculate BPM
Add Volume parameter in instrument editor (close #29)
Update README: link to releases
Update README: more visible download link
Write sequencer module

All the step sequencer global state is now inside a struct.
Add "make zip" task
Bump version to 0.8
Add missing comments in main app loop
Move all step advancement code to seq_tick()
Write Sequencer UI module
Refactor as MVC

Define 2 controllers, one for each mode (pattern editor, instrument
editor). Sequencer is the only model (for now), and each mode has its
own view module.
Add nicer default INSTRS.DAT
Move Makefile to root and font files to fonts/
Add XCF (Gimp) source files for fonts
Pattern Editor View