Exploratory development for https://github.com/FriendsOfSymfony/FOSElasticaBundle/issues/410
Don't need postRemove.
Refactor to a single Listener class.  Update tests.
Re-add renamed Listener.
pre/postFlush configuration. Update documentation.
Remove upgrade doc.  Merk will add manually.
Remove debug.
Use constants of corresponding events classes rather than making assumption about string values.
Use bulk insert.  Still working on bulk update/delete which is not yet suppored in Elastica.
Merge remote-tracking branch 'upstream/master'
Bulk update.  Still working on bulk delete for indexes and types in Elastica.
Bulk delete
Merge remote-tracking branch 'upstream/master'
Update tests
Merge pull request #415 from nurikabe/master

Refactoring to update ElasticSearch index in postFush