Wrote combine method for Clusters class, it combines two clusters into one.
Implemented assignment probability for the cluster function.
Changed Clusters init method to use super(), calls dict.__init__
Added copy function to Clusters class.
Just some docstring stuff.
Changed clusters variable to clustered.
Added bic method to Sorter class which returns the Baysian Information Criteria value.
Added split method to Sorter class.
Added combine method to Sorter class.
Added save method to Sorter class.
Added a line to Sorter.__repr__ that recalculates params['K'] using the length of Sorter.clusters.

I had to do this because for some reason, the correct value for K in
params wasn't working when I created the Sorters using the parallel
engines of IPython.
Just an extra line.
Renamed map_parallel to map.