tippecanoe main writes pmtiles output. [#10]

* detect output format using suffix
* after mbtiles is done writing, replace with pmtiles based on map/image tables.
* add method to write_json for writing json sub-object.

pmtiles_file.hpp

@@ -0,0 +1,16 @@
+#ifndef PMTILES_FILE_HPP
+#define PMTILES_FILE_HPP
+
+#include "pmtiles/pmtiles.hpp"
+#include "mbtiles.hpp"
+
+bool pmtiles_has_suffix(const char *filename);
+void check_pmtiles(const char *filename, char **argv);
+
+void mbtiles_map_image_to_pmtiles(char *dbname, metadata m, bool tile_compression, bool quiet, bool quiet_progress);
+
+std::vector<pmtiles::entry_zxy> pmtiles_entries_tms(const char *pmtiles_map, int minzoom, int maxzoom);
+std::pair<uint64_t, uint32_t> pmtiles_get_tile(const char *pmtiles_map, int z, int x, int y);
+sqlite3 *pmtilesmeta2tmp(const char *fname, const char *pmtiles_map);
+
+#endif