#41-add-flag-support-to-cppmagics

I just implement the asked mechanism: the subcommands clang, gcc, anycppcompiler and clang-tidy only get the print_command variable and display it. Both '--print-command' and '-p' options are accepted. NB: parsing option decorator doesn't seem to work well when our own commands contain options so the processing of --print-command is hardcoded for now. When several options are needed, I intend to reimplement this mechanism with argparse.

Close #41 (closed).