Experiment with chroma from metadata.
Add metadata field to dump format.
About a 90% solution to enumerating the tiles for a map.

The problem is that it can miss some when long vectors span
multiple tiles, because the points within the vector aren't
sorted.
Enumeration fixes:

* Use the declared zoom from encoding as the default for enumeration

* Look as deep as shows up in the rendering (display + 9) for how
  many files to check for points.
Treat chromacity as a vector instead of a scalar

so that when there are competing claims for a pixel, the strongest
can win, or they can compromise somewhere with less saturation.
Desaturate when there is color conflict. No color when there are no meta bits.
Oops. Remember to convert to and from radians.
Make color range a command-line flag.