Infinite loop fixes, minimizing changes to behavior (#345)

* Divide-and-conquer polygon cleaning

* Catch the case where the gap can't be increased further

* Catch the case where we try to keep impossibly many features

* Make label points earlier in the tiling process

* Another case where it could try to drop even after already limiting.

* And do not coalesce on impossibly small geometries

* Add missing return

* Update version and changelog

geometry.hpp

@@ -173,4 +173,7 @@ void get_quadkey_bounds(long long xmin, long long ymin, long long xmax, long lon
 
 clipbbox parse_clip_poly(std::string arg);
 
+bool line_is_too_small(drawvec const &geometry, int z, int detail);
+void coalesce_polygon(drawvec &geom, bool scale_up);
+
 #endif