Add support for fatalError()

[hlineholm]

A fatal error in Swift

fatalError("An error \(error) occurred")

could be converted to

throw Exception("An error $error occurred")

[angelolloqui]

Thanks.

I think this will go when I make the Foundation converter plugin, in which I plan to replace things that are not part of the language itself but from the foundation types.

[angelolloqui]

Added a very simple version of this as part of 8b94a81