* :bug:`548` Restore ``--non-interactive`` as a flag not expecting an
argument.

* :feature:`547` Add support for specifying ``--non-interactive`` as an
environment variable.

* :feature:`336` When a client certificate is indicated, all password
processing is disabled.
* :feature:`489` Add ``--non-interactive`` flag to abort upload rather than
interactively prompt if credentials are missing.
* :feature:`524` Twine now unconditionally requires the keyring library
and no longer supports uninstalling ``keyring`` as a means to disable
that functionality. Instead, use ``keyring --disable`` keyring functionality
if necessary.
* :feature:`518` Add Python 3.8 to classifiers.
* :bug:`332 major` More robust handling of server response in
``--skip-existing``

* :feature:`437` Twine now requires Python 3.6 or later. Use pip
9 or pin to "twine<2" to install twine on older Python versions.
* :bug:`491 major` Require requests 2.20 or later to avoid reported security
vulnerabilities in earlier releases.

* :feature:`488` Improved output on ``check`` command:
Prints a message when there are no distributions given to check.
Improved handling of errors in a distribution's markup, avoiding
messages flowing through to the next distribution's errors.

* :feature:`456` Better error handling and gpg2 fallback if gpg not available.
* :bug:`341 major` Fail more gracefully when encountering bad metadata
* :feature:`459` Show Warehouse URL after uploading a package
* :feature:`310` Now provide a more meaningful error on redirect during upload.

* :bug:`452 major` Restore prompts while retaining support for suppressing
prompts.
* :bug:`447 major` Avoid requests-toolbelt to 0.9.0 to prevent attempting to
use
openssl when it isn't available.
* :feature:`427` Add disable_progress_bar option to disable tqdm.
* :feature:`426` Allow defining an empty username and password in .pypirc.
* :bug:`441 major` Only install pyblake2 if needed.
* :bug:`444 major` Use io.StringIO instead of StringIO.
* :bug:`436 major` Use modern Python language features.
* :support:`439` Refactor tox env and travis config.
* :bug:`435 major` Specify python_requires in setup.py
* :bug:`432 major` Use https URLs everywhere.
* :bug:`428 major` Fix --skip-existing for Nexus Repos.
* :feature:`419` Support keyring.get_credential.
* :feature:`418` Support keyring.get_username_and_password.
* :bug:`421 major` Remove unnecessary usage of readme_render.markdown.
* :feature:`416` Add Python 3.7 to classifiers.
* :bug:`412 major` Don't crash if there's no package description.
* :bug:`408 major` Fix keyring support.