make rotating boxes lovely pinky pink
Add slide args to synths:

* Each synth now has a slide arg which is 0 by default.
* Slide represents the amount of time to slide between the previous note and the next (when synth is controlled)
* Synths with cutoff arg now also have a corresponding cutoff_slide arg

Example:

s = play 50, :sustain, 3
sleep 0.5
s.control :note, 62, :slide, 2