RPCalc is a programmable, stack based, reverse polish notation calculator
An operation in rpcalc looks like this:

	4 5 *

'4' and '5' push the numbers 4 and 5 to the top of the stack, and the '*' operator multiplies the 
4 and the 5 and pushes 20 to the stack where the 4 whilst also reducing the stack size by 1, makeing 20 the head of the stack.

Functions can also be declared in rpcalc:

	:foo + + ;

This defines a function call foo that performs the addition operation twice. A colon followed by an identifier begins a function
definition, and a semi-colon finishes the function defintion. When a function is called, all operations inside the function
are performed in order.

Currently, a few functions are defined in rpcalc, but the end goal is to have rpcalc load up functions from a file at runtime.