refcycle 0.2.0

This is a minor release, containing a few new helper methods and
bugfixes. Highlights include the shortest_path and shortest_cycle
methods, improved annotations, and fixes for performance bugs that make
linear-time algorithms take quadratic time or worse.

Features

• Support Python 3.4 through 3.6. (#65, #55)

• New ObjectGraph methods: shortest_cycle, find_by_typename
  and count_by_typename. (#64)

• New shortest_path method. (#61)

• Reduce memory usage of the AnnotatedGraph object by adding slots
  to the AnnotatedEdge and AnnotatedVertex types.

• Add specific annotation for module objects.

• Add specific annotations for getset_descriptor objects.

Changes

• Use the current line number instead of the first line number in
  the annotations for frame objects. (#50)

Fixes

• Fix quadratic-time behaviour in DirectedGraph.full_subgraph. (#63)

• Fix non-linear (exponential, in extreme cases) running time in
  descendants and ancestors methods. (#62)

• Fix annotations for functions with no __name__ attribute. (#59)

• In Python 2, fix annotations for bound methods with no im_class
  attribute. (#56)

• Fix annotations for some peculiar frame objects whose f_locals dict
  has been replaced with a dict-like object. (The Enaml package does this.) (#51)

• Fix missing annotation for f_trace on frames. This was causing one
  of the tests to fail when run under coverage. (#41)