Add Launchy option to launch spec results instead of reading terminal output.

The HTML format for rspec is beautiful.  The master branch of guard-rspec does not have an option to launch the html output in a browser, as far as I can tell.  

So I have implemented the :launchy option which will use Launchy to launch the rspec output file.

Please consider this feature as I think it will be valuable to many users to view the HTML format of rspec vs. the console output. 

thanks!
Don