Add 'export_image' method to 'ObjectGraph'.
Add tests for explicit and implicit format determination.
Update CHANGES.
Merge from master.
Be strict about writing .DOT file in UTF8.
utf-8 seems to be the more standard name for the encoding.
Avoid the need for a temporary file by sending the graph straight to stdin.  (Thanks, @sjagoe.)
Move export_image functionality to the AnnotatedGraph.
Merge pull request #19 from mdickinson/feature-export-image

Add 'export_image' method to 'ObjectGraph'.
Fix slow full_subgraph, which iterated over *all* the edges of the graph.
Merge pull request #26 from mdickinson/fix-slow-full-subgraph

Fix slow full_subgraph.
Rename export_json to to_json.
Re-implement export_json for exporting to a file.
Merge remote-tracking branch 'origin/master' into feature-import-json
Fix PEP8 violations in the Sphinx conf.py.
Merge pull request #27 from mdickinson/feature-import-json

Add import_json; repurpose export_json.
Add AnnotatedGraph to refcycle exports.
Merge pull request #28 from mdickinson/fix-missing-annotated-graph-export

Add AnnotatedGraph to refcycle exports.
ancestors and descendants were missing some nodes; use breadth-first search instead of depth-first to fix this.
Merge pull request #31 from mdickinson/fix-ancestors-and-descendants

Fix depth limited searches in `ancestors` and `descendants` methods.