Remove standalone pytest run_tests.py bundle Newer pytest doesn't support generating stand alone testing bundles. Python 3.9 generates errors running the current run_tests.py. Changed doc to use pythonX -m pytest test/ and some light directions on how to install pytest. Thanks to jerrykan for recommendations on how to do the doc updates.

#!/usr/bin/env python
from __future__ import print_function
import zlib, base64, sys
print(base64.encodestring(zlib.compress(sys.stdin.read())))