Externalizing polygon shard detection (#146)

* Start of externalizing polygon shard detection

* Completely untested external quicksort

* Add unit test for external quicksort

* Remember to clean up temporary files

* Sort and scan the vertices

* Bring over more vertex logic

* Make nodes from vertices

* Checkpoint on switching over to global shared nodes

* Do the thing

* Revert unintended change to coalesced linestring behavior

* Take shared nodes into account in early simplification

* Let it do more sorting in memory

* Fix overnoding of collinear linestrings

* Remove duplicate nodes, since only duplicate vertices now matter

* Remember to delete temporary files

* Fix out of bounds memory access below, apparently

* Fix the actual undefined behavior

* Still running out of memory in one case. Find out where.

* Forgot the conditional

* Try again to make it not run out of memory

* Update version and changelog

sort.hpp

@@ -0,0 +1,6 @@
+#ifndef SORT_HPP
+#define SORT_HPP
+
+void fqsort(std::vector<FILE *> &inputs, size_t width, int (*cmp)(const void *, const void *), FILE *out, size_t mem);
+
+#endif