^ (square) doesn't work for multiplication

[elsoroka]

Example code:

using Satisfiability
@satvariable(a, Int)
a*a # works
a^2 # doesn't work

I think for user-friendliness, ^ should produce a multiplication operation. Making an issue to think if there are other math operations that aren't part of the SMT-LIB standard but reasonably map to SMT-LIB operations.