Clean up FOR variables from symbol table after use

They were causing issues when generating the print symbol list, as
there was no match in the symbol case map.
Restored (44) comma fix representation for DM

It was referenced by testing/test.z80s, and could exist in other
source modules. It doesn't cause a problem to keep it for backwards
compatibility. "make test" now works once again.
Updated to support Python 3

Changed to use new print function in Python 3, and import print
function from __future__ for Python 2.6+ compatibility without
tuple printing issues.
Make it clear this is not the official pyz80 release

Added link back to GitHub for modification details and updates.