Ability to apply 'this' command to a path

Adds a -P or --repo-path command to check if a specified path is in the got
configuration

Not yet documented, need feedback before continuing.  My use case is a tool that finds all my git repos under a specified path and checks if they are in gitgot.  I could chdir to the repo and then just run ```this``` but adding support for a path seemed like a reasonable addition.

This might better be implemented as a ```that``` command instead of an argument to ```this``` but the implementation of ```this``` and ```that``` would be damn near identical.

Thoughts?  Is this functionality something you would be interested in?