tor-config-path: new crate containing moved `tor_config::path`

This moves the path module from tor-config to a new tor-config-path crate. Currently tor-config re-exports CfgPath and CfgPathError from tor-config-path, but I'll update all of the imports in a follow-up MR.

This also comments-out a test in tor-config-path that relies on internal implementation details of tor-config. I'm not sure yet what to do about this test, and I don't really know what the test is trying to do. I'll try to improve this in a follow-up MR as well.

(If this is merged, I'll make an issue for the above follow ups and work on that.)