Color.fromRandom

This finishes up the work started by @andre-nunes in #1038.  Since he's working on KML for GSoC, I wanted him to stay focused on that.  This change now uses the `MersenneTwister` mentioned by @shunter and finishes up the doc and specs.

@shunter I wasn't sure what exactly had to go into license.md, since the header for mersenne-twister.js has some additional comments in addition to the license.