Add DCSN-2 Script

[chrisib]

Adds a loopable, random gate sequencer based on the Robaux DCSN3. Because we have fewer outputs, this uses a binary tree structure instead of a ternary one. But otherwise the principle is the same: on every clock cycle one child, and one of its children is selected as "on" and all other outputs are "off". Similar to the Turing Machine, the probability of the pattern repeating or randomly changing can be controlled via knob & CV input.

Adds the ellipse function to the oled documentation & derived classes, as it makes drawing circles & ellipses easier.