python v3.7 (#639)

* add unit test for mbtiles missing center/bounds
* code and file cleanup
* more details in python README.md

python/pmtiles/README.md

@@ -1,6 +1,21 @@
 # pmtiles
 
-`pip install pmtiles`
+```sh
+pip install pmtiles
+```
+
+## Running Tests
+
+```sh
+python -m unittest test/test_*
+```
+
+## Uploading build
+
+```sh
+python -m build
+twine upload dist/*
+```
 
 ## Status