Implemented compileJJTree task

This is an initial implementation of a JJTree task feature. Added tests which passes and tested on my project. I will make some more tests with some JavaCC only project to ensure they are still working great.

Once we agree that it's ok with you, I will update `README.md` file.

* It is now possible to compile a JJTree file to re-use it afterward
   in when compiling JavaCC.
* Test resources have been moved in two distinct directories: one
   for `javacc` and another one for `jjtree`.

Regards,
Matt
No I was not aware. I generated the projects using gradle, so I thought they were already configured to use project specific settings. I imported the relevant config and re-run formatter on all files.

With the next text resource feature in Gradle 2.2, we could think about having project specific settings out of the box.