Generic Custom Object Support + Generic Parsing Updates + Streaming Examples

Multiples updates!

1. Generic Custom Objects have been added, allowing any STIX 2.x x- object can be parsed into a "CustomObject" allowing you to parse anything you may find in your bundle and is STIX 2.x compliant ! 🎉

2. Added a small fix to the StixParser class to support better Java Generics

3. Added Tests in the src/test/stix/bundle/BundleSpec to show usage of Streaming large STIX datasets, Reading and writing STIX json.