Add enum34 as a dependency.
Make edge_dfs use a new Direction enum.
Add option for 'reverse' traversals.
Violating 80 character rule to make doctests happy.
Use 'forward' and 'reverse' strings to indicate traversal direction.
Remove enum import statement.
Use import * in traversal submodule.
Docstring changes for edge_dfs and company.
Merge branch 'edgedfs' into findcycle
Docstring updates.