extremely small refactorings

Very small refactorings and few code annotations (todos and note, in doxygen format).
They are preparations for heavier and deeper code changes, with more performances impacts.

Reorganization of source code into a dedicated folder tree containing only source code.

Also add support for cmake build system. qtcreator project is probably broken, since some files have been added. (a win for cmake: no need to explicitly add files)