README
https://github.com/tmpvar/vec2.js
https://github.com/jnordberg/geometry.js
https://github.com/okcupid/node-geom2d/
https://github.com/STRd6/matrix.js
http://paulbourke.net/geometry
http://www.codeproject.com/Articles/15573/2D-Polygon-Collision-Detection
http://softsurfer.com/algorithm_archive.htm