Support `Int` and `UInt` wider than 64 bits.

Emboss should support types like `UInt:128`.

The main open issue is figuring out what type to use for wide integers in C++: there is no support for them in the C++11 (or 14, 17, 20, or 23) standards, so we would likely need to provide our own implementation and/or a way for users to insert their preferred wide integer library.

This feature requires #40 to be implemented, either first or in tandem.