Adds standalone driver emboss-format for compiler/front_end/format.py

[reventlov]

This should both help visibility for the formatter and make it easier for non-Bazel users to use it.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[reventlov]

I updated my CLA to add my GitHub username, so hopefully the CLA check will pass now.

[jasongraffius]

@reventlov I re-ran the CLA scan, looks like your Github username is validating now in the CLA, but not the email in the author line of the commits.

[reventlov]

@jasongraffius I think I have gotten that email address (ben-emboss@xn13.com) in the right place to make the CLA bot happy now.

[jasongraffius]

Thanks for this! I have a couple of quick questions