Fix invalid reference to self in test

[ci skip]
Added: update() method for ProvDocument and ProvBundle
Added: convenient assertions methods for ProvEntity, ProvActivity, and ProvAgent
Merge branch 'master' of https://github.com/trungdong/prov
Fixed: Inclusion of namespaces in unified document
Merge branch 'master' into prov-xml

Conflicts:
	prov/tests/test_extras.py