Added necessary operator overloads I missed before, fixed calculator
example. It works like a charm for integer operations in int64_t's
range like a charm. I'll add paren and FP support one day, but for
now, I think that I should just write list parser now, and I shall
be able to move to developing the assembler (at last... :D).

I'll probably need to add a way to specific constructor functor
one day, but it would probably not be necessary for the assembler
iself, so it isn't a priority right now.