rio-pmtiles python package [#338] (#542)

Add rio-pmtiles command line tool. [#338]

This is derived from the original mapbox/rio-mbtiles implementation, with changes:

* output PMTiles only instead of MBTiles.
* Python 3.7+ only.
* remove --implementation, --image-dump, --append/--overwrite, --covers features.
* bump dependency versions.
* better progress reporting; add pyroaring. 
* update README and license texts.
* rio-pmtiles v0.0.6 on PyPI

python/pmtiles/examples/create_raster_example.py

@@ -0,0 +1,36 @@
+# Generates a raster tile archive for conformance testing.
+
+from urllib.request import Request, urlopen
+from pmtiles.tile import zxy_to_tileid, tileid_to_zxy, TileType, Compression
+from pmtiles.writer import Writer
+
+acc = 0
+
+with open("terrarium_z0-3.pmtiles", "wb") as f:
+    writer = Writer(f)
+
+    for tileid in range(0, zxy_to_tileid(4, 0, 0)):
+        acc += 1
+        z, x, y = tileid_to_zxy(tileid)
+        req = Request(f"https://s3.amazonaws.com/elevation-tiles-prod/terrarium/{z}/{x}/{y}.png")
+        with urlopen(req) as f:
+            writer.write_tile(tileid, f.read())
+
+    writer.finalize(
+        {
+            "tile_type": TileType.PNG,
+            "tile_compression": Compression.NONE,
+            "min_zoom": 0,
+            "max_zoom": 3,
+            "min_lon_e7": int(-180.0 * 10000000),
+            "min_lat_e7": int(-85.0 * 10000000),
+            "max_lon_e7": int(180.0 * 10000000),
+            "max_lat_e7": int(85.0 * 10000000),
+            "center_zoom": 0,
+            "center_lon_e7": 0,
+            "center_lat_e7": 0,
+        },
+        {
+            "attribution": '<a href="https://github.com/tilezen/joerd/blob/master/docs/attribution.md">Tilezen Joerd: Attribution</a>'
+        },
+    )