Add command to check current file on save

This pull request adds a command that runs rubocop (and shows simplified output in a tooltip) when you save a file. This way I don't have to remember to manually run rubocop - I'll see it's output automatically. This is helpful for organizations that have strict rules about checking in style violations.

Also added was a fix to the existing "Check Current File" command to set it's output to `showAsHTML` (currently it's set to "Display Nothing"). When I added the bundle to TextMate and tried to test it out, I was a little confused as to why I wasn't seeing output.