Make `Fn::Equals` accept any Token type

[jfklingler]

The docs say

value
    A value of any type that you want to compare.

So I believe that Fn::Equals should support more than just String arguments. I haven't tried to make this change and I can't quite resolve all of the types in my head, but I think we should be able to do something along the lines of

case class `Fn::Equals`[T](a: Token[T], b: Token[T])
  extends NestableAmazonFunctionCall[String]("Fn::Equals")
{type CFBackingType = (Token[T], Token[T]) ; val arguments = (a, b)}

I suspect there will be troubles with the serialization though.