Bringing the readme up to date with the current code.
Add note about working examples to readme.
Removed extra _ in on_complete note.
Improve note about Context.on_complete.
Merge pull request #16 from WebFilings/context-splitup-import-fix

Make sure public API methods are imported into context.
Merge pull request #15 from WebFilings/readme-cleanup

Readme cleanup
Merge branch 'master' of github.com:johnlockwood-wf/furious into ndb-persist

Conflicts:
	README.md
added batch_id. removed erroneous placement of _persistence_id into kwargs of Async.from_dict. added Marker.from_async.
MarkerPersist.from_marker.
preparing for no initial persistence of leaf nodes.
preventing non-root markers from being persisted.
check for done code doesn't assume child entities exist.
disabled persisting MarkerTree in the call to persist and instead inserted an async task to do it later, but that seemed to perform worse.
passed on IndexError for _execution.py because if a an async was processed twice, it would raise an error.
disabled persisting a MarkerTree a all. that along with only initially persisting the root and internal vertex markers, the /context example runs around 200ms instead of 1100ms
made saving the MarkerTree optional during the persist and off by default