Experiment with optimizer to detect arcs from linear segments

[voneiden]

Been there done that before but now that it looks like pyclipper is the defacto way to go, it could be interesting to have an optimizer which attempts to detect arcs (within a certain tolerance) from linear segments so that we can actually have G2 and G3 commands.

Performance is a concern, especially for large programs, so this should be fast and some perf testing should also be done to see if it's viable.