Added verify-related and verify-proceeding.

I've added two methods: `rspec-verify-related` and `rspec-verify-proceeding`.

`rspec-verify-related` is more fuzzy than `rspec-verify` and can match several files. This is useful for me because I have some tests under `./spec/controller` and `./spec/requests/` that test the same controller.

`rspec-verify-proceeding` will run the current spec file and the one after it. This is really useful in combination with `--fail-fast` in rspec: the suite will run until a test fails, then I can fix the test troublesome test, and then proceed with the rest of the suite starting from the spec file that failed. It saves me a lot of time since one of our test suite takes 5min to run.

Cheerios!