Replace int types with fixed point

[jameshegarty]

Replace the uint/int types with fixed point types. Have them behave like regular int types when the exponent is 0. This will cut down on the number of types we have to support.

Have 2 sets of math operators, one that expands bits to keep all precision (floating-point emulation behavior), and one that keeps bits the same (this should be the default probably).

For now, if fixed point exponent doesn't match, just fail in typechecking.

We may also want another variant, which is saturating ops?