github_56: using bulk_upsert in oplog manager
github_56: added bulk_upsert method to elastic doc manager + tests
github_57: DocManager is aware of namespace set
github_57: tests for mongo_doc_manager created with a namespace_set

github_57: added kwargs to all DocManager constructors
github_56: fixed docstrings on bulk_upsert methods
github_56: better handling of bulk-insert of empty document sequence
README documentation for bulk_upsert DocManager method
Merge branch 'github_56'