Just a short todo, notes on how to get it done.
Stubbed out global error corrections as an abstract class.  I'm not
really happy with the way it's going to look.  Specifically, the
observe method is going to be nasty, and will only really make sense
with eagerly computed heuristics.
Added global corrections to the FF heuristic as an example of how we
might implement global corrections using multiple inheritance.  I'm
not really happy with it, since there's a bunch of code that would
need to be copy and pasted for all heuristics.
Merge pull request #6 from jordanthayer/master

Example Global Correction Heuristic