SAMPLES!

Added arbitrary looping waveform playback capabilities. Users must create their own poly_sample struct. The wave type name 'poly_sample' has been renamed to 'poly_onesample' to be paired with 'poly_loopsample' as a cleaner distinction. The appropriate poly_sample struct definition, in addition to poly_set_sample(int i, poly_sample *s) functions have been added. 

An example program (which we should have much more of) has been placed in examples. I recommend we populate this with more things.

Now we can finally create those grunge-waves.