added documentation for return type to `draw_networkx_nodes`,
`draw_networkx_edges`, `draw_networkx_labels`, `draw_networkx_edge_labels`.
pep8 compliance work
pep8 compliance work
modified `nx_pylab.draw()` so that it does not draw node labels as the
documentation claims.
Merge pull request #935 from tacaswell/draw_return_doc

Draw return doc
Merge pull request #936 from tacaswell/draw_bug

Draw bug