Stack machine simulation.

Requires clang 3.1.

* Usage:
	** ./runner [-v] [-f asm_file]
	*** -v: verbose, step through code
	*** -f: asm file to assemble and run

* Instructions:

	** PUSH
		Pushes the value in the next code instruction.

	** POP
		Discards the top stack value.

	** NOP
		Do nothing.

	** HLT
		Halt the machine.

	** OUT
		Pops a value and prints the value to stdout as a char.

	** STORE
		Pops a value, pops an address, then places the value in mem
		at the addres.

	** LOAD
		Pops an address, loads that value from memory, then pushes
		that value.

	** ADD
		Pops two values and pushes the sum.

	** SUB
		Pops two values and pushes the difference.

	** MUL
		Pops two values and pushes the product.

	** DIV
		Pops two values and pushes the quotient and remainder.

	** JMP
		Sets the CPU instruction pointer to the value popped.

	** JZ
		Pops an address and pops a value. If the value is zero,
		moves cpu->ip to the address.

	** JNZ
		Pops an address and pops a value. If the value is not zero,
		moves cpu->ip to the address.

	** CALL
		Pops an address and pushes to the return pointer stack.
		Moves instruction pointer to that address.

	** RET
		Pops an address from the return pointer stack and moves
		the instruct pointer there.

	** DUP
		Duplicates the value on the top of the stack.

	** SWAP
		Swaps the values of the top two values on the stack.

	** INT
		Registers an interrupt handler. The handler address and the
		resource address are popped from the stack.

	** DEBUG
		Put the cpu into debug mode.

* Hardware:

	** KBD
		Awaits a keystroke and then pushes it onto the stack.