python-stix v1.1.0.0

* Updated bindings to support STIX v1.1
* Updated existing API classes to support STIX v1.1
* Added `stix.utils` package with `idgen`, `nsparser`, and `parser` modules
* Namespace output cleanup
* Added `EntityParser` class that checks STIX document version conformance
* Changed `from_xml()` behavior to output API object instead of tuple
* Added initial cuts at Threat Actor and Incident classes