Kotlin specific documentation

[lleyton]

If we want to make Kotlin (and the framework/DSL we build on it) our flagship developer experience, we're going to need some damn good documentation. Depends on #26 and #27.

[leinardi]

Just a suggestion: mkdocs and Dokka are pretty neat tools to write/generate Kotlin docs:

https://gtk-kn.github.io/gtk-kn/user-guide/hello-world/
https://gtk-kn.github.io/gtk-kn/dokka/
https://squidfunk.github.io/mkdocs-material/

[lleyton]

Thanks!