Add an option to extend zooms if still dropping, but with a limit (#131)

* Add an option to extend zooms if still dropping, but with a limit

* At least when to overzoom, even if not actually doing it yet

* Refactor to give tile-join access to overzoom()

* Didn't work, but *might* have worked

* OK, it did something now

* Ah, there's the bug!

* Hook up pmtiles and dirtiles as overzooming sources

* Add command line option to enable or disable overzooming

* Add (currently broken) test of overzooming in tile-join

* Slightly more abstraction for the tile-join readers

* Factor out duplicated code

* Move construction into a constructor

* More changing accessors to methods

* Reduce magic

* Start tracking a list of the tiles at maxzoom

* I think it worked?

* Add missing #include

* Fix sequence of overzoomed tiles (Y sorts backwards for TMS)

* Don't spend memory on overzooming when we aren't going to use it

* Diff rather than cmp, in the hope of figuring out this broken test

* Keep full coordinate precision if we might extend zooms

* Try a slightly different byte limit

* Make drop-densest more consistent across tile boundaries

* Also affects this test

* Does it behave any differently if it can extend forever?

* I think the discrepancy is a thread-safety problem here

* Revert "Does it behave any differently if it can extend forever?"

This reverts commit 0dff0a0acc.

* Lost this change to the test

* This time for sure!

* Revert "Also affects this test"

This reverts commit cd1f7c2e78.

* Revert "Make drop-densest more consistent across tile boundaries"

This reverts commit 563f7d2bc2.

* Revert "Try a slightly different byte limit"

This reverts commit 2e271213d6.

* Add some more explanatory comments

* Amend the join-test to detect my current bug

* Allow overzooming to complete the zoom if it ever starts

* Forgot to correct the test

* Update changelog and version

* Cleanups from code review

* Remove version number from fixture to fix test

geometry.hpp

@@ -3,6 +3,8 @@
 
 #include <vector>
 #include <atomic>
+#include <set>
+#include <string>
 #include <sqlite3.h>
 #include <stdio.h>
 
@@ -88,4 +90,7 @@ drawvec clip_point(drawvec &geom, long long x1, long long y1, long long x2, long
 void visvalingam(drawvec &ls, size_t start, size_t end, double threshold, size_t retain);
 int pnpoly(const drawvec &vert, size_t start, size_t nvert, long long testx, long long testy);
 
+std::string overzoom(std::string s, int oz, int ox, int oy, int nz, int nx, int ny,
+		     int detail, int buffer, std::set<std::string> const &keep);
+
 #endif