Changed Stores.get_path_stores to Stores.get_value_path_stores to make to_python compatible with both simple values and Element.
Updated tests.
CheckKeys accepts ref_key_name.
Fixed class attribute name string_validator_instance in constraints.AddKeyRef.
Element.to_dict: added test for empty list to before writing out empty '#text'.
Removed special treatment for root element, now gets name prefix, like every other element.
Changed validated attributes to Ordered Dict.
Removed separation of name space prefix from tag in element.
unified validation in ElementSchema.
Changed element._value_to_string to _value_to_unicode.
Fixed py3 related import issues in test_utils.
Implemented build method to all validator classes, added unit tests.
Added placeholders build methods to ElementSchema and SequenceSchema.
Increased coverage for constraints and validators to 100%.
Added build methods to validators and schemas including tests.
Merge branch 'release/0.1'