feature request: pickle-ability

I'm kind of surprised no-one else has requested this: how about making all
matplotlib objects picklable?

The ability to save a plot to disk as a python object and recall it at a
later date, or send a live matplotlib figure over a network socket would
be really useful. I often have plots I need to make small changes to at a
later date.

Getting the pickling of all the C-objects right might be tricky, I guess.