 DOC: `Edge()` initializer also accepts `Node` objects for `src` and `dst`
 DOC: `Edge()` initializer also accepts `Node` objects for `src` and `dst`

Commit triggered by comments at:
    http://stackoverflow.com/questions/6953957/edges-between-two-subgraphs-in-pydot

erocarrera/pydot,pydot/pydot