("Pair of two numbers") Cont. Allow registering custom literal values (#740)

[msparkles]

@schungx It would seem that the idea of packing the two i32's into one i64 would not really work-- if the less significant part of the i64 has a negative number, when doing arithmetic the carry of the result would go out of its bound and into the more significant part, resulting in a deviation of 1 from intended result.