Total order planner

[bcorfman]

I've made some additions to planning.py to implement a total order planner with examples. I also made a small change to utils.py to include a partition function that I used in the planner.

The code can be viewed in my fork here:
https://github.com/bcorfman/aima-python/blob/master/planning.py
https://github.com/bcorfman/aima-python/blob/master/utils.py

[norvig]

This looks very good! I'd be happy to have this added. Sorry for the delay in responding, @bcorfman

[bcorfman]

NP. The code could always use some improvement, but I'm glad you found it useful. If there's something further you want me to do, let me know.