Polyphonic Sequencer

Polyphonic Sequencer is the natural progression from Smooth Sequencer. I adapted the original logic to a Voice class, which can "sing" a maximum of one note at any point in the sequence. Naturally, then an array of Voices represents a sequence where multiple notes can be played in polyphony across the sequence.

I then adpated code from Scales which allowed 2 things:

1. The Y axis now represents musical pitch linearly. That is, a movement a certain distance along the y axis will always result in the same step in pitch along the music scale. This is in contrast to Smooth Sequencer where the y axis represented frequency, which has an exponential relationship with musical pitch.
2. The sequences can now be quantised! The scale is set to C major pentatonic.

Since we can quantise the pitch, It seemed sensible to also allow quantisation of time. This was much simpler than pitch quantisation. We begin by breaking up the length of the sequence into a number of time steps (16 in this case). Then, at any point along the sequence, instead of accessing the current note we access the note that's at the start of the current time step! In practise this means that when we play a sequence, notes may only change, begin or end at the beginning of a time step.