Use Jonty

[peter-tackage]

I've replaced the handcrafted list of fields with a Kotlin based annotation processor which creates the appropriate list in a Kotlin file. Review of the annotation processor: https://github.com/peter-tackage/jonty also welcomed/encouraged.

I should add that generating Kotlin via an annotation processor for Android brings out the worst in the build system; hence the many long explanations littered over the build.gradle.

[peter-tackage]

@maritoast I'd still like to fix the Kotlin companion object field bug, which will require changes to Jonty.