Put dot serialization/plotting back in, no attrs support for now.
Throw an error on not having the necessary combination of concepts.
Merge pull request #22 from rsofaer/dot

Dot serialization on BGL without attrs.
has -> contains for Set
use do syntax in to_dot
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.