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/bin/pmtiles-show

@@ -0,0 +1,21 @@
+#!/usr/bin/env python
+
+import sys
+import pprint
+from pmtiles.reader import Reader, MmapSource
+
+if len(sys.argv) <= 1:
+    print("Usage: pmtiles-show PMTILES_FILE")
+    print("Usage: pmtiles-show PMTILES_FILE Z X Y")
+    exit(1)
+
+with open(sys.argv[1], "r+b") as f:
+    reader = Reader(MmapSource(f))
+    if len(sys.argv) == 2:
+        pprint.pprint(reader.header())
+        pprint.pprint(reader.metadata())
+    else:
+        z = int(sys.argv[2])
+        x = int(sys.argv[3])
+        y = int(sys.argv[4])
+        sys.stdout.buffer.write(reader.get(z, x, y))