With a new thread to handle queue-clearing instead of process(), retriggering lots of samples won't zombify us.  But still more work to do..
Fixes the retrigger bug. Added a loop specifically for user interrupts in disk_thread().  This new do..while() wraps the current do..while() loop for soundfile repeats set by ficus_loop() and the while() loop check to see if process() is still doing work.
Merge branch 'fix_retrigger_sample' into dev
Fixed a bug where audio samples would keep looping even if you called ficus_killplayback() on them.  Some README cleanup happened too.