OptionVersion class

[Peter]

There is a class for --help but no class for --version.

Class should collect data from config.h when available and also allow user to override and set data explicitly (e.g. copyright year). Output and behaviour see e.g. svndigest.

The collection from config.h is a bit tricky as it has to be collected from the application config.h, which implies these data cannot be compiled into the lib but has to be inlined.

[Peter]

Of note, GCS mandates that first line in --version output should not depend on argv[0].