This fixes the circular cutout issue described in #32. Regions were previously stored as a collection of points, now they are stored as a collection of line and arc primitives.
per #33
the issue was trying to re-open the temporary file. it works on everything but windows. I've changed it to seek to the beginning and read from the file without re-opening, which should fix the issue.
This branch allows a pure cairo based render for both PNG and SVG.
Cairo backend is mostly the same but with improved support for
configurable scale, orientation and inverted color drawing.
API is not yet final.
This fixes the exception referenced in #12. Still need to add rendering
code for rectangle aperture lines and arcs.
Rectangle strokes will be drawn as polygons by the rendering backends.
