WIP: overlapping regions splitting functionality

[russelldj]

The goal of this is to make a set of potentially-overlapping polygons nonoverlapping. The definition for how to split is as follows: for any given point covered my multiple polygons, assign it to the polygon for which it is furthest interior from the nearest edge. The code so far only handles this for the pairwise case using the following steps:

• Identify the overlapping region
• Subtract this region from both input polygons to obtain the unambiguous regions
• Add additional points to the boundary using segmentize
• Create the veronoi tessellation to determine the region closest to each point
• Dissolve these regions based on which polygon boundary the point was from

I haven't rerun this recently, but I think it was having numerical issues.