TODO-list decompyle

For Release 2.2:
easy:
- add options for tabwidth, TAB, etc.
- Check whether decompyle can read 1.6 and 2.0 bytecode
medium:
- find out how to verify optimized bytecode (.pyo)
- extend test_nested_scopes with parts form cgitb.html()
- test EXTENDED_ARG -> how?
hard:
- try to find a way to verify 'for ...' if byte-code is generated by
  older versions of Python.

Planned for future releases:
- use weak references in Parser to save memory (maybe)
- avoid unnecessary parentesis in expressions
