Figure out how to handle concave polygons

[frewsxcv]

https://github.com/PistonDevelopers/graphics/issues/860

@Ralith on #rust-gamedev recommended https://en.wikipedia.org/wiki/Delaunay_triangulation

[frewsxcv]

Some links:

• https://github.com/mapbox/earcut
• https://hal.inria.fr/inria-00405478v4/document
• http://www.cs.wustl.edu/~taoju/research/triangulate_final.pdf

That last one in particular seems promising

[frewsxcv]

More links:

• https://github.com/mitsuhiko/rust-poly2tri/blob/master/src/lib.rs
• https://github.com/tynril/rtriangulate/blob/master/src/lib.rs
• https://github.com/jhasse/poly2tri
• https://en.wikipedia.org/wiki/Polygon_triangulation
• https://www.cs.ucsb.edu/~suri/cs235/Triangulation.pdf
• https://stackoverflow.com/questions/5247994/simple-2d-polygon-triangulation
• https://www.google.com/search?q=sidel+algorithm&ie=utf-8&oe=utf-8

[frewsxcv]

Done in https://github.com/frewsxcv/rgis/commit/874a5f8bed839572f8cd50e3869368aecd139db2