Add Part.make_var()

For creating a symbol and registering bounds
Move variable creation to optimization module

optimization now has a variable factory, producing
variables and defaultdict-like variable containers

Plus code for generating constraints directly relating
to variables, e.g. upper and lower bounds, SOS1, SOS2,
etc. More will probably be added, e.g. integer constraint.

test.py shows a basic example of how to use new functionality
Remove some new and old junk
Add .pyc to .gitignore