1. It's impossible to use methods that modify parameters in swig so
I extend it in wrapper
2. Simplify GetArcAngle() and fix the bug where it lies about 360
degree arc to be 0 degrees.
We no longer have any knowledge of the original start/end of the arc,
since SetArcAngleAndEnd swaps the start and end to ensure the arc is
always clockwise at the end.
Adds a method EDA_SHAPE::EndsSwapped() to notify whether the start/end
point of the shape were swapped.