Starting random graphs
Fix a bug in building small world graphs
Fix the random tests and a bug in Watts-Strogatz graph generation.  They plot quite nicely now.
Sort of fix attribute modification in random graphs, this will fail unless attributes are removed from the Vertex hashing function.
Change to using test instead of assert, all broken right now.
Fix small mistake in graphs.rst
Add Erdos/Renyi (uniform) random graphs.