GC-47: Add support for Python 3.13:

- Simplify the option presence checks in functional tests to avoid
having to deal with differences in output between Python 3.13 and
older versions (similar checks are already in place for things like
key specification anyway). For more details, see this commit:

https://github.com/python/cpython/commit/c4a2e8a2c5188c3288d57b80852e92c83f46f6f3

GC-44: Added support for Python 3.12:

- Updated documentation.
- Updated release notes.
- Updated supported Python versions in package configuration file.
- Updated Python versions used for tests.

GC-43: Added support for Python 3.11:

- Updated documentation.
- Updated release notes.
- Updated supported Python versions in package configuration file.
- Updated Python versions used for tests.

GC-42: Added support for Python 3.10:

- Updated documentation.
- Updated release notes.
- Updated functional tests (small tweak for help output change).
- Added signing key for the Python 3.10 and 3.11 releases.
- Updated supported Python versions in package configuration file.
- Updated Python versions used for tests.

GC-45: Drop support for Python 3.5, 3.6, and 3.7:

- Updated documentation, removing references to versions as being
supported.
- Switched the Vagrant test machine to Debian Bullseye (still in LTS
support) to match the main development environment.
- Updated functional tests for output changes in OpenSSL CLI from
Debian Bullseye.
- Updated Tox configuration and instructions.
- Dropped workaround for Python 3.5.
- Updated package requirements.
- Updated release notes.

GC-39: Added support for Python 3.9:

- Updated release notes
- Updated functional test for changes in help output in Python 3.9.
- Updated comments on public signing keys used for validating the
Python archives when using Vagrant provisioning.
- Updated supported Python versions in package configuration file.
- Updated Python versions used for tests.

GC-33: Added support for Python 3.8:

- Updated release notes.
- Updated documentation.
- Updated Python versions used for tests.
- Updated supported Python versions in package configuration file.

GC-35: Drop support for Python 3.4:

- Updated documentation, removing Python 3.4 as supported version.
- Updated documentation to include support for Python 3.7 (this was
already supported, but documentation did not list it in a couple of
places).
- Updated Tox configuration with list of supported Python
versions.
- Build Python 3.5.x for full test against all Python versions in
order to make it independent of underlying distribution Python
version.
- Update package requirements.
- Updated release notes.