Renamed Generator to Definitions, further refactoring ahead

Next step will be moving generator code from Definitions into
its own class, probably using some kind of abstract interface class
Moved generator code in Definitions into "NuriaGenerator"

Also added a skeleton for the JsonGenerator which will come next.
Implemented the JSON generator

There are still some bugs and TODOs left, but apart from that this
implementation is pretty functional already. This also requires
some changes elsewhere to make the generator more useful.
Added JSON generation option to main.cpp (-j<File>)

Sidenote, the current argument parser process is ugly and should
be replaced with the LLVM argument parser which uses a nice template
based approach.