Bump for 0.3.2
Use stevedore for dynamic check inclusion

Allow checks to be created outside of doc8
and use stevedore to load these check objects
and use them when checking.
Use a deque to avoid keeping all the scanned files alive

Avoid keeping all the files that have been read and scanned
in memory by use a deque and popping files off after they
have been read (this allows the gc to clean them up).