Resolving Ambiguities

All the code for Marching Squares 3 is done, all that's left now is to write the actual tutorial.

The last part was resolving the ambiguous cells - cases 6 and 9 - in a reasonable way. Is there a diagonal connection, or not? Sharp features allow us to answer this question. It's a bit involved though, as we have to deal with up to two sharp features in a single cell.