Making more flexible code holder
Rough cut for do everything solve wrapper
Putting code in dict
Cleaning up
Cleaning up AD operator interface
Implement __int__ for AD

Not sure this is really the best way to manage it, but seems to work
Initialize Codegen._code = {} in base
Adding ordering to ._code keys for printing
Bugfix
Printing source more simply

I didn't get into trying to get C codegen to print headers, etc.  But
should work for Matlab and Python.
Little clean
Merge pull request #32 from chinasaur/codegen/1

Codegen/1
some renaming so things make sense
some notes about nodes and terms and expressions
rolled in latest dim setter changes.
broke out some parts of a program into separate class.
another reorg. halfway done.
added some test case structure
high level reorg complete. still need to fix expr and canonicalization