multitasking - running more than one ender build at the time

For my project I had to build two different ender library, one for the desktop and the other one for the mobile.

I kept the common declaration used in grunt for the Gruntfile.js task :
```javascript
ender: {
  desktop: {
    output: "scripts/vendor/ender",
    dependencies: ["morpheus", "bean", "bonzo", "domready", "qwery", "valentine"]
  },
  mobile: {
    output: "scripts/vendor/ender.mobile",
    dependencies: ["bean", "bonzo", "domready", "qwery"]
  }
}
```
so you can run only one task by using `$ grunt ender:mobile` or all of them with the default command `$ grunt ender`