Add path & focus support

- Adds `RunNearsetSpec` command
- Includes the path in the command string ([card](https://trello.com/c/OZyXWosa/12-detect-path-to-current-file))
- Includes the focus (line number) when running `RunNearestSpec` ([card](https://trello.com/c/MZdY5nyk/9-detect-focus-line-number-for-rspec-tests))
- Clear leading space if preloader not defined ([card](https://trello.com/c/sWBujyko/16-kill-leading-space-when-no-preloader-is-used))
- Do not wrap the interpolated `{command}` in quotes.