1. Split compression parameter generation and compression parameter
packing. This gives a good performance boost, since we don't pack every
single time we compress. The error is computed each time, and only the
best parameters are packed.
2. Allow the shape selection function to specify up to ten shapes to
try for compression. We were already doing this kind of hackily where
we allowed both a three and two partition shape. This makes it a little
cleaner and exposes it to the user.
We suffered another performance hit. This time it comes from the fact
that we're copying around a lot of data based on what partition we're
choosing. We can get rid of this a tad by only copying the data that we
need once and then using getters/setters that selectively pull from
an array based on our shape index.
