Publishing to PyPI

1. In CHANGELOG.md, change [UNRELEASED] to version number and date
2. In shiny/__init__.py, change version to new version number
3. On the Releases page, create a new release following the same tag and title convention as the previous releases.
4. Once step 3 succeeds, the package will be on PyPI.
5. Go to CHANGELOG.md and create a new [UNRELEASED] section.
6. Go to shiny/__init__.py and add a .9000 suffix to the version number.