Doc, whitespace cleanup
Change interface to RCM

Allow a heuristic function to pick the start node for RCM instead of a specific node. Deprecate start= keyword for heuristic=
Add docs for RCM
Use generator and min for performance
Merge pull request #1113 from hagberg/rcm-order-bug

Cuthill-Mckee - ordering heuristic, fixes #1073 and #1068.