Add transactional complete write before callbacks
Improve mark complete
Cover race condition where marker has been deleted
Add initial persistence logic
Add some tweaks from the PR
Fix broken tests, clean up APIs and add comments
Merge branch 'context-completion-persist-results' into completion_integration

Conflicts:
	furious/extras/appengine/ndb_persistence.py
Handle post merge errors
Add back in inserting tasks external to the tx
 Clean up whitespace and doc strings
Add tests for ndb_persistence

Add unit tests for ndb_persistence module
Add apache header to test_ndb_persistence
Switch to batch method that doesn't require a filter

Instead of using izip_longest instead use a slice batch method so we can avoid
an extra filter of None values.
Merge branch 'context-completion-persist-results' into completion_integration

Conflicts:
	furious/extras/appengine/ndb_persistence.py
Address cr comments in async.py
Address cr comments in context.py
Address comments from cr to ndb_persistence.py
Update results example based on cr
Address comments from cr for simple example.
Remove Test ndb model from test