1) An actual distance of 0 is still a collision, even if the allowed
distance is 0.
2) Be consitent about edges and interiors. Everyone expect the edge
of a RECT to be part of the RECT; same with a CIRCLE. SHAPE_POLY_SET
shouldn't be any different. (And SHAPE_LINE_CHAIN was a split-
personality with the edge considered part of it for Collide() but not
for PointInside()).
* Split up the thirdparty code into the thirdparty folder (#3637)
* Create a new kimath static library containing all the math functions
This is part of cleaning the build system for #1906.
