Add initial Kotlin runtime support

[seabaylea]

Add initial support for Kotlin. This supports two API formats:

1. JSON in / JSON out, using the gson package:

   fun main(args: JsonObject) : JsonObject {}

2. Data class in / data class out, e.g.:

   data class User(
    val id: String
   )
   
   fun main(user: User) : User {
    return user
   }

This only supports sync/blocking APIs at the moment - async can be added but there should be a discussion on the use of callbacks vs Futures, etc.

[csantanapr]

Could you add the hello world example you have in your comment in the README?