Migration to Kotlin based Build system

[b69644445-cpu]

Android is evolving and now "mandates" the use of Kotlin as built system.
I tries to rebuild Markwon from scratch in Android Studio and I got issues with the outdated build system (Gradle uses too old libraries)

So I tried to update the build system.

Note: as it is a huge change, I tried it first on my fork and I need help to fix some issues

[b69644445-cpu]

Please have a look at https://github.com/b69644445-cpu/Markwon for the repo as I am struck at the moment
I will open a pull request once issues got fixed