VM ptr type refactor

added the following types and constants:
VM::ptr // a pointer to a memory address in the VM's stack
VM::ptr_size // size of VM::ptr
VM::ptr_max // the largest pointer address you can have

the ScriptStack makes use of this pointers. ATM, VM::ptr is an unsigned
char, making the VM an 8 bit machine. To change this, all you have to do
is change the base type of VM::ptr, and everything else should update
automagically
attempting to write nodes