Implement:

* include faster normal distribution normal2

* more distributions 

  * Continous distributions 
    - Beta distribution
      http://en.wikipedia.org/wiki/Beta_distribution
    - Maxwell distribution
      http://mathworld.wolfram.com/MaxwellDistribution.html
    - Kolmogorov-Smirnov distribution
      http://en.wikipedia.org/wiki/Kolmogorov-Smirnov
    - Levy distribution
      http://en.wikipedia.org/wiki/L%C3%A9vy_distribution

  * and other distributions, see
    http://en.wikipedia.org/wiki/List_of_probability_distributions

* ISAAC generator
  http://burtleburtle.net/bob/rand/isaacafa.html

