Updated todo-list

- add support for expressions in LHS nodes (rulecompiler.py)
- implement retract, Done [2006-10-26]
- make Assert and Retract available in RHSs, Done [2006-10-26]
- implement Not and Exists.
- implement support for the CLIPS language,
- implement an interactive shell for pyRete, Done [2006-11-24]
- improve the Rete Network Viewer.