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, jasmine, reload browser on file change
To initialize, run: 
```
guard init
guard init cucumber
guard init rspec
guard init jasmine
```

To integrate zeus into Guard, edit Guardfile and add `cmd: 'zeus'` for rspec and `command_prefix: 'zeus'` for cucumber.
any reason why this was included? Don't we already have `pry`?