Add Xamarin Studio (MonoDevelop) Cask.
user
```ruby
class XamarinStudio < Cask
  url 'http://download.xamarin.com/studio/Mac/XamarinStudio-4.0.13-38.dmg'
  homepage 'http://xamarin.com/studio'
  version '4.0.13-38'
  sha1 '8c2ab4ae42576c7d2ff7689e0eff35a983544e8c'
  link 'Xamarin Studio.app'
end
```
assistant