Circle collidepolygon() and Polygon collidecircle()

[itzpr3d4t0r]

Should close #180 and #175.

Added:

• Circle collidepolygon() function, with optional only_edges param (only does edge collision) defaulting to False
• Polygon collidecircle() function, with optional only_edges param (only does edge collision) defaulting to False
• Internal pgCollision_CirclePolygon and _pgCollision_PolygonPoint_opt helper (faster version of
  pgCollision_PolygonPoint that assumes the point passed not to be one of the polygon's vertices)
• Docs and tests
• Python example program

Changed:

• geometry.pyi Coordinate from Union[Tuple[float, float], Sequence[float], Vector2, Tuple[int, int]] to Union[Sequence[float, float], Vector2, Sequence[int, int]]

Removed

• 6 c_api slots in geometry.c needlessly occupied by pgCollision_LineLine, pgIntersection_LineLine, pgCollision_LineCircle, pgCollision_CircleCircle, pgCollision_RectLine, pgCollision_RectCircle

This PR is also a nice example of how to use the newly added Polygon internal functionality for working with polygons outside the polygon module.
A screenshot from the example: