Send to kindle recipe added.
user
```ruby
class Send_to_kindle < Cask
  url 'http://s3.amazonaws.com/sendtokindle/SendToKindleForMac-installer-v1.0.0.218.pkg'
  homepage 'http://www.amazon.com/gp/sendtokindle/mac'
  version '1.0.0.218'
  sha1 'a1c2759d220e707b12cfefa8fcd1f58f5d3165cf'
  install 'SendToKindleForMac-installer-v1.0.0.218.pkg'
end
```
assistant