2d pattern weld and simplification

[petrasvestartas]

Mapping

• Bug fix: Point Welding

Point welding bug for the case: Point A at (5.99, 6.0) and Point B at (6.01, 6.0).
When comparing these two points the distance between them is 0.02 but the generated key was wrong. It can be one integer to the left or right (5 or 6). Solution: check neighbor 9 surrounding buckets to avoid integer rounding error.

• New Feature - Bounday Polygon Simplification

After boolean intersection the pattern is merged with boundary polygons. This is often not wanted.
2D method is implemented via Clipper. Simplification is made by comparing polygon after boolean intersection and before. If the points lie on the initial polygon we keep them. Additionally we add an option to keep arbitrary points from a user given points or boundary valence points.

simplify_borders = True
fixed_points = [...] # mesh vertex indices

simplify_borders = True

simply_borders = False

[tomvanmele]

perhaps still mark parameters with a default value as optional in the docstings...