Add quadratic bezier curve support by converting quadratic spline to
cubic spline.

The conversion follows the formula:
CP1 = P0 + 2/3 * (P1 - P0)
CP2 = P2 + 2/3 * (P1 - P2)

where:
- P0, P1, P2 are quadratic control points
- CP1, CP2 are the resulting cubic control points

Ref:
https://fontforge.org/docs/techref/bezier.html#converting-truetype-to-postscript

Allow drawing elliptical arcs by specifying end points instead of
center point, following some common vector graphic endpoint
parameterization format.

Ref:
https://www.w3.org/TR/SVG/implnote.html