Create sm.py

This (sm.py) is a "stack machine": an interpreter for an extensible
reverse Polish instruction set.  For example: rev up the Python 3 
interpreter, say ">>> from sm import *", and then say ">>> run('1 2 add')".
You can turn the verbosity flag by saying ">>> set_verbosity(b)",
where b is Ture or False.

Run "python3 sm.py" for more information.  For more examples, 
run "python3 sm.py -e", and for some documentation, run 
'python3 sm.py -d".  To run internal tests, use "python3 sm.py -t".  

This is a rough first cut, and it is mostly for playing around
to illustrate and (for me) to understand some CS ideas.  However, 
one could conceivably use it, after customizing the instruction set, 
as an on-board interpreter.  See the examples.  

To add to the instruction set, add an entry to the dictionary 'ops'.

Note that one can define new functions within this little language.
For example, "run('defprog cube dup dup mul mul /defprog 3 cube')"
define a new instruction, "cube", and then applies it the integer 3.