Add ability to manually parse user agents

It would be cool if we could parse userAgents manually (E.g. I'm currently working on a site where you can see your sessions and it would be nice to provide a little icon. To find out the browser type I would like to use the $device api).

I think you just need to export the function, then we can all use it. Otherwise something like `$device.parse(myUserAgent).isAndroid` would be cool.