[cmake-developers] (Experimental) Refactored extra-generators

[Alexander Neundorf]

Hi,

I spent a few hours on the extra-generators, and you can find the result here 
on github:
https://github.com/neundorf/CMake/tree/RefactorExtraGeneratorsExperimental 

In this branch, the extra-generators are not tied anymore hardcoded to the 
generators (so the generator list is short again), but each extra-generator 
can be enabled and disabled via a cmake option 
CMAKE_ENABLE_EXTRA_GENERATOR_<name>.
I.e. for every build directory zero, one or multiple extra-generators can be 
enabled and disabled (in an existing build tree).

This would e.g. also be suitable for a generic JSON-generator.

The code on github is not ready to be merged, and unfortunately I don't have 
the time to bring it into mergeable state, including tests, documentation, 
etc.

But if somebody is interested, you can have a look and give it a try.

Alex