Added Mersenne Prime Twister random number generator

I was using FastRandom to create randomly placed cities/roads/etc. However, it sometimes produced funny random numbers which didn't look very random to me.

So I started searching for a more sophisticated implementation and found a Java implementation of the popular Mersenne Prime Twister, written by [Sean Luke](http://www.cs.gmu.edu/~sean/research/). It is only one file licenced unter the [3-clause BSD](http://en.wikipedia.org/wiki/BSD_licenses#3-clause_license_.28.22Revised_BSD_License.22.2C_.22New_BSD_License.22.2C_or_.22Modified_BSD_License.22.29). It generates high quality pseudo-random numbers at high speed.

I've written a JUnit test that verifies its correctness and compares its speed to java.util.random and FastRandom.

I also compiled the source into a tiny jar and put it under engine/libs. Is that how it's done?