Bugfix in find_root:

The coarse stage was being too conservative: the 10% buffer was going
higher than the max value of the field, causing no reduction in
problem size for the interpolation step.

The wiggle room the in coarse solve has been removed.
Changes to the actual analysis.

Primarily the addition of the vorticity field (as yvslice). Also
no longer clips the data going into Grid.add(), but instead clips
the plots themselves.