Add Xamarin Platform v5.0.1 (build 3)

Xamarin's new app installer to install version 5 (and above) of Xamarin Studio with Xamarin iOS,
Xamarin Android, and Xamarin Mac. This is meant as a replacement for the current Xamarin casks: `xamarin-android`, `xamarin-ios`, and `xamarin-studio`, locked at version 4.

I need help with the uninstall logic. I need to remove folders `/Applications/Xamarin Studio.app` and `~/Library/Developer/Xamarin`. It's currently giving an error upon running `brew cask uninstall xamarin-platform`