Release

Update __version__ in slackviewer/__init__.py to the new version
Commit this change as "Release 0.9.0" to master, as an example
Create a release on GitHub with the new version (e.g., 0.9.0) targeting master
git pull locally
git clean -fdx dist to clean anything already in the dist/ directory
Run python setup.py sdist (in the correct environment) to create the package to upload
Run twine upload dist/* to push to PyPI