FFI in nitg-g

This branch can be interpreted in 5 main sections:

* General fixes are first
* FFI implementation
* Updating the use of the FFI in the library
* Add annotations "pkgconfig" and "c_.*_compiler"
* Updating the use of the FFI in the library (general and pkgconfigs)

Jenkins results: http://gresil.org/jenkins/job/CI%20Alexis/23/

A future pull request will add support for the C++ language, and the next one the Opengles 2, x11 and egl modules.