Functional visitor, Java 8, comments

[nightscape]

Hi @timowest,

I've dug much deeper than I initially planned and made quite some changes to scalagen, but I hope they pay off:

• I replaced the Maven build by an SBT one which gives much nicer compilation speed and other goodies and is the de facto standard for most Scala projects.
• I transformed the statefull ScalaDumpVisitor into a stateless ScalaStringVisitor which instead of modifying a local SourcePrinter returns Strings in all visit methods.
• Formatting is now handled by Scalafmt which gives much more flexibility on how to format code and reduces the complexity of scalagen a little.
• The Java parser library is updated to a version that supports Java 8 and the corresponding visit methods implemented, so we should be able to transform Java 8 code (most likely there's some bugs in there, which we can fix as we discover them)
• Comments are copied as good as possible. There's still some edge cases where they can get lost, especially when multiple comments occur in a row.

It would be great if you could have a look at this so we can start discussing on how to integrate and release this. If I have time, I'll publish a build on Bintray so that people can already start trying this out and finding bugs :wink:

Phew, that was a journey! :smile:

[matozoid]

As the maintainer of JavaParser I would say: PLEASE merge this because your dependency is way out of date!