Introduce a DSL to offer an easier way to define transformation templates

[fabiocarvalho777]

Explore easier ways to define transformation templates. One alternative solution would be using a DSL, instead of Java.

These are the motivations for this story:

1. Make transformation template definition less verbose, easier and closer to natural language
2. Simplify and make it easy to develop and maintain extensions
3. Remove the Java requirement for extension development
4. Keep backward compatibility (if possible)
5. Support every feature present in the current transformation template definition mechanism (Java based)
6. Provide end user documentation

Kotlin and Spek

Probably the best option to develop this DSL would be Kotlin. An alternative would be Groovy. Kotlin seems to be better because it has better Java interoperability and is a more modern language. Also, if Kotlin is the chosen one, Spek could be used for tests.