Executing my assembler app.

- Executing my full hand-written assembly-language program:
multiplying a couple of numbers, calling a function, incorporating
results from that function.  I have my own concept of a program
counter, operation stack(s), and a method stack.  Woo-hoo!

- Streamlined my “assembly language” since the previous checkin:
removed some methods that seemed gratuitous, combining them with others.

Issues:

- This is perhaps grossly inefficient.  I’m just trying to get things
working at all, at the moment.

- There are several hacks and approximations.  E.g., I haven’t yet
resolved how to handle an internal concept of a “pointer,” so I have
the “multiply” method — my only math method — just keep dereferencing
whatever it got until it figures out whether it’s a number.

- I’m not doing the *math* myself.  I’m depending on the host language
(Objective-C, at the moment) for that.  I’m not yet sure whether this
needs to go in my VM, but it doesn’t need to be here yet.