Drop or retain whole multiplier clusters when dropping as needed (#198)

* Prep to track conditions other than just "dropped" or "kept"

* Count up instead of down

* Drop or retain whole multiplier clusters based on their first feature

* Calculate a global feature dropping sequence

* Switch over to using the drop sequence for drop-fraction

* Remove unused arguments for the old drop-fraction implementation

* Fix copy-and-paste bugs, update tests

* Properly incorporate feature_minzoom into the drop sequence, I hope

* Rename drop_by to drop_sequence

* See if sorting within clusters fixes filter stability between zooms

* Remove very chatty debug print

* Update changelog and version

* Use named constants instead of numbers for feature dropping/keeping

* Add comment to explain purpose and method of bit reversal

CHANGELOG.md

@@ -1,3 +1,9 @@
+# 2.43.0
+
+* Change -fraction-as-needed feature dropping to be consistent across tiles and zoom levels, and to follow the same pattern as point dropping by zoom level
+* With -as-needed feature dropping, drop or retain entire multiplier clusters instead of individual features
+* Sort the features within each multiplier cluster by its retention priority, for more consistency between zoom levels in filtered feature choice
+
 # 2.42.0
 
 * Improve tiling speed