Swing Playback implementation using staff texts

Swing playback using staff texts implemented, facilitating local control over swing parameters. Also added tests for the same.
Ok, assuming IEEE float, as per http://www.h-schmidt.net/FloatConverter/IEEE754.html the values 0.5 and 0.25 do have an exact representation. But other innocent looking valoes like 0.1 and 0.3 don't...