Usage of the -d opion corrected
Giving an error when a wrong -d option is given.
Made some error mesages more consistent.
Corrected usage of the exit call, in case of an error: exit(1) otherwise exit(0).
A closer look should be made on exitDoxygen as it does not contain any exit statements and it is unclear (to me) when it is used.
Merge pull request #38 from albert-github/feature/code_debug

Usage of the -d opion corrected