This is a yet-to-be-proved (I.e. I think it is) Turing complete Reverse
Polish Notation calculator

The language is quite simple:

 * +  -- add the top two operands
 * -  -- subtract the top two operands
 * *  -- multiply the top two operands
 * ^  -- clear the top operand
 * &  -- Swap the top two operands
 * $  -- duplicate the top two operands
 * [  -- enter a loop if the top is not zero
 * ]  -- exit the loop
 * ?  -- skip an instruction if the top is not zero
 * !  -- print debugging information
 * ,  -- store at the addr on the top of the stack, the next value on the stack
 * .  -- load from the addr at the top of the stack.


Notable bugs:
 
 * Whitespace: It hates white space
 * Input strings containing ?] have the potential to cause a memory leak
 * It will parse strings like "A2+" to (65-48) + 2. The -48 is because of
   shifting to get a numerical value for ascii chars 1-0