This is an alternative method for fitting a curve which incrementally simplifies the curve, then re-fits.
Generally gives better results, also improves corner detection.
Add a new fallback method that uses offset distance from the curve to the line between both points,
for freehand drawing it typically only fives minor improvements (1-3% fewer points),
for curve dissolve the improvements are more noticeable.
Take curvature into account when calculating handle length.
Gives significantly better results for curve dissolve and 10-20% more efficient freehand drawing.
This will be used for calculating bezier curves from freehand drawing,
may be used for other areas too.
Original code from GraphicsGems, 1990 (FitCurve.c),
with updates from OpenToonz, under 3 clause BSD license.
with own minor modifications for integration with Blender:
- support adding extra custom-data.
- improved handle clamping.
