Elm version using BigNums.

Elm version using BigNums.

This went pretty smoothly, I just followed the compiler errors after
substituting Integer for Int in the type definition.

The only tricky thing is that the div and mod functions for Integer
return Maybe Integer rather than just Integer, so I need to wrap those
or something?  (For now I just put in add to get it to compile.)

Oh, and "not equal" is not correct? The compiler didn't complain.