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)
You do not need to keep reinitializing `logger` by calling `logging.getLogger(__name__)` when you want to output a logging message. You just need to do that once per method. You can just move this line up to the top of this method and then remove all other instances of `logger = logging.getLogger(__name__)` from it.