Curve fitting

I've shelved the SVG conversion code for now, as although it's a fun challenge, it's somewhat worthless longer term.

I see my next few activities as:
- Develop a GCode pre-processor that sits between Skeinforge and the printer host, which will convert incoming continuous paths into splines
- Add an acceleration calculation into the pre-processor to provide acceleration "hints" to the firmware
- Modify firmware to support acceleration hints, with graceful degradation to current acceleration algorithm
- Implement tolerance-driven path smoothing to the pre-processor

Might take a while to get through all that, but I've made a start tonight by working up a basic algorithm to take a sequence of linear line segments and convert them to a sequence of bezier curves using a modified form of the Finite Difference approach from http://en.wikipedia.org/wiki/Cubic_Hermite_spline. Currently it smooths all segments, but next I'll add an inter-segment angle calculation and only smooth segments with a small angle (perhaps <10 degrees). Then just need to wire that to a GCode parser and that should yield a functioning, albeit very simplistic, pre-processor.