STIX-Java-Kotlin 2.1 update

[Stephen Russett <stephen@digitalstate.ca>]

Hello all

I have released the first draft of 2.1:

https://github.com/StephenOTT/STIX-Java/tree/2.1

This update implements STIX with kotlin. 

Spec is about 40% implemented. 

Targets are kotlin, java JVM and native.

Always looking for collaborators, so if you are working on something similar, please reach out.  

Enjoy