Migrate build to use Gradle Kotlin DSL

[skuzzle]

Migrate Gradle build to use the Kotlin DSL (#97)

Checklist:

• [x] Generating Readme/Release notes work
  • [x] Publishing Readme/Release notes to repo root works
• [x] Generating Asdcii doc works
  • [x] References/Includes are correctly processed
  • [x] Publishing to repo root works
• [x] Generating POM works
• [x] Publishing to maven local works
• [ ] Release works on CI
• [x] Gathering code coverage works
  • [x] Coveralls publishing works
• [x] // TODO comments resolved
• [x] Verify cacheability / UP_TO_DATE checks
• [x] Check dependencies