Enhance ``api.content.transition`` with the ability to transition from
the current state to a given state without knowing the transition path.
refs. #162
fix flake8 failure
make sure we have either transition or to_state, never both
Move most recent change to the top.
correct doc string for _wf_transitions_for
Merge pull request #164 from plone/issue_162

Enhance ``api.content.transition``