sampler addded with tests cases and documentation.

Added support for kernels: 
 * Radial Basis Function Kernel (RBFSampler)
 * Additive Chi Squared Kernel (AdditiveChi2Sampler)
 * Skewed Chi Squared Kernel (SkewedChi2Sampler)
Since this is all run through `nose`, you should actually just use print statements here. The results will get captured by `nose` and only be displayed when there's an error.