add feature to generate config file

[Peter Johansson]

add parameter flag --generate-config=file

where default is to write to std::cout

When this flag is set only config file is generated and no "digesting" of the repo.

If the file already exist config file should not be over-written but just updated, i.e. add recently added features in config file that are missing in old config file. See Doxygen for an example.

[Peter Johansson]

(In [229]) Modified behaviour of Configuration. Fixes #114, #115, #116