Ubiquerg

Changed
- Expanded `mkabs` function to handle more cases
- Allow `is_url` to work on Path objects
- Remove `mock` test requirement in favor of importing `unittest.mock as mock`

Added
- Experimental support for three-locking.

Fixed
- Incorrect read of registry path. [Issue 35](https://github.com/pepkit/ubiquerg/issues/35)

Fixed
- `is_url` function; [Issue 32](https://github.com/pepkit/ubiquerg/issues/32)

Changed
- file locking enhancements

Added
- file locking utilities:
- `create_lock`
- `remove_lock`
- `make_lock_path`
- `create_file_racefree`
- `wait_for_lock`