contrib: new, a directory for non-mainstream functionalities This new 'contrib' hierarchy will be a good place were to move implementation/support for obsolescent features we are not yet ready to remove completely, or were to leave experimental or third-party features to cook before their eventual inclusion in the automake core. * contrib: New directory. * contrib/README: New file. * contrib/Makefile.am: New file. (EXTRA_DIST): Distribute README.