Extra coordinate precision; feature ordering; compression improvements

* Add an option to retain extra coordinate precision at maxzoom

* Make sure not to shift away the extra detail from coordinates

* Add an option to convert double-precision attributes to single

* Sort attribute values in tiles to make them compress a little better

* Slightly improve polygon simplification

By choosing a point that would be retained after simplification
to be the start/end point that always gets retained

* I regret making all of these tests involve polygons

* Add an option to specify the size of tiny polygons

* Fix accidental requiring of argument for --single-precision

* Guard against duplicate points when generating "sizes" for them

* Restore the intended behavior that tiny polygons don't get simplified

* Make the extra detail settable rather than always maximizing it

* Revert "Improve maxzoom guessing for tightly-clustered point data sources (#4)"

This reverts commit fec5e8354c.

* Add an option to prevent choosing a base zoom higher than the maxzoom

* Keep the drop rate high enough when the basezoom gets constrained

* Revert "Revert "Improve maxzoom guessing for tightly-clustered point data sources (#4)""

This reverts commit db6bc27d9e.

* Add --order-by and --order-descending options

* Accept multiple --order-by and --order-descending-by sort keys

tests/dateline/out/-z5.json

@@ -8,6 +8,7 @@
 "maxzoom": "5",
 "minzoom": "0",
 "name": "tests/dateline/out/-z5.json.check.mbtiles",
+"strategies": "[ {  }, {  }, {  }, { \"tiny_polygons\": 1 }, {  }, { \"tiny_polygons\": 1 } ]",
 "type": "overlay",
 "version": "2"
 }, "features": [