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/rio-pmtiles/tests/conftest.py

@@ -0,0 +1,63 @@
+import functools
+import operator
+import os
+import shutil
+import sys
+
+import py
+import pytest
+import rasterio
+
+from unittest import mock
+
+test_files = [
+    os.path.join(os.path.dirname(__file__), p)
+    for p in [
+        "data/RGB.byte.tif",
+        "data/RGBA.byte.tif",
+        "data/rgb-193f513.vrt",
+        "data/rgb-fa48952.vrt",
+    ]
+]
+
+
+def pytest_cmdline_main(config):
+    # Bail if the test raster data is not present. Test data is not
+    # distributed with sdists since 0.12.
+    if functools.reduce(operator.and_, map(os.path.exists, test_files)):
+        print("Test data present.")
+    else:
+        print("Test data not present. See download directions in tests/README.txt")
+        sys.exit(1)
+
+
+@pytest.fixture(scope="function")
+def data(tmpdir):
+    """A temporary directory containing a copy of the files in data."""
+    datadir = tmpdir.ensure("tests/data", dir=True)
+    for filename in test_files:
+        shutil.copy(filename, str(datadir))
+    return datadir
+
+
+@pytest.fixture(scope="function")
+def empty_data(tmpdir):
+    """A temporary directory containing a folder with an empty data file."""
+    filename = test_files[0]
+    out_filename = os.path.join(str(tmpdir), "empty.tif")
+    with rasterio.open(filename, "r") as src:
+        with rasterio.open(out_filename, "w", **src.meta) as dst:
+            pass
+    return out_filename
+
+
+@pytest.fixture()
+def rgba_cutline_path():
+    """Path to a GeoJSON rhombus within the extents of RGBA.byte.tif"""
+    return os.path.join(os.path.dirname(__file__), "data/rgba_cutline.geojson")
+
+
+@pytest.fixture()
+def rgba_points_path():
+    """Path to a pair of GeoJSON points. This is not a valid cutline."""
+    return os.path.join(os.path.dirname(__file__), "data/rgba_points.geojson")