Guard integration

Guard watches your file system and runs specs or other commands when it changes. (similar to autotest)
https://github.com/guard/guard

Plugins included: run rspec, cucumber, reload browser on file change
To run Guard: `bundle exec guard -G config/Guardfile`

To integrate zeus into Guard, edit Guardfile and add `cmd: 'zeus'` for rspec and `command_prefix: 'zeus'` for cucumber.