style: stop using deprecated getargspec for rpc

python3: migrate setup.py

style: remove new-style class code from the Python2 days

demo: properly escape screen command parameters

bug: fix wrong sending of HMAC header causing test failure

setup: indicate minimum Python versions

doc: update dependencies in readme

Fix permission for ovpn-client and ovpn-server

vcs: add test-related generated files to gitignore