Hammer CLI

Instead of:

:modules:
- hammer_cli_foreman
etc

it would be nice to have something like $confdir/hammer.modules.d/ where a modules could add config of their own (e.g. enable foreman module by creating $confdir/hammer.modules.d/hammer_cli_foreman). This makes it much easier to enable modules from separate OS packages (as they can just drop a file in place, instead of sed'ing the main hammer config file)