Multiprocessing for genmatrix()
Moved `num_processes` param to HierarchicalClustering constructor
Moved util.genmatrix() into matrix.ItemItemMatrix

more complex code deserves its own submodule
Complying with @exhuma's comments/requests
Now we actually need to use the new Matrix changes :)

Also moving num_processes away from Matrix constructor, into genmatrix() call, since it makes more sense there
Fix for tests list
Merge remote-tracking branch 'loisaidasam/feature/multiprocessing' into release-1.2.0

Conflicts:
	cluster/util.py  used loisaidasams version.
Documentation update.
Added an example for KMeansClustering.
Added tests for gihub issue #11

See https://github.com/exhuma/python-cluster/issues/11