First beta release of new Go CLI

This is the first release of a new CLI tool for exercism.io. The Go based tool will allow non-Ruby folks to more easily interact with the site.

As this is the first beta release, please expect rough spots. If you find rough spots, please file a bug on the issues page or submit a pull request.

This release requires a fix to be applied to the server to get beta version of CLI tools to work. If you are getting 500's when submitting an assignment, please hold off until the server gets updated. Otherwise, all other functionality should work.

Thanks!