Support for ThreeTenBp

[masc3d]

relating to #7, would it make sense to also add support for https://github.com/ThreeTen/threetenbp?

It can be used as a drop-in replacement for android < API Level 26, allowing very smooth (package replace) migration once a project moves to >= 26.

Would you accept PR for this?

[debop]

Sure, please PR

[masc3d]

would you agree to improve packages for major future release? eg

com.github.debop.koda.time -> standard java.time
com.github.debop.koda.joda -> joda
com.github.debop.koda.threetenbp

[debop]

Split module

java-time ( for standard java.time in jdk 8)
koda-time for joda

You can add threetenbp module