Perlin Noise

Implementation of Ken Perlin's noise algorithm.

References:
http://www.noisemachine.com/talk1/index.html
http://code.google.com/p/fractalterraingeneration/wiki/Perlin_Noise
http://webstaff.itn.liu.se/~stegu/TNM022-2005/perlinnoiselinks/perlin-noise-math-faq.html