Twine release version 1.11.0

* #319: Support Metadata 2.1 (PEP 566), including Markdown for description fields.
* #320: Remove PyPI as default register package index.
* #322: Raise exception if attempting upload to deprecated legacy PyPI URLs.
* #269: Avoid uploading to PyPI when given alternate repository URL, and require protocol prefix (such as `https://`) in repository_url.
* #318: Update PyPI URLs.
* #314: Add new maintainer, release checklists.

For past releases, see https://twine.readthedocs.io/en/latest/changelog.html .