3.0.0-dev.1

Related pr: #295

Deprecations

PR #290: For semver 3.0.0-alpha0:
- Remove anything related to Python2
- In tox.ini and .travis.yml Remove targets py27, py34, py35, and pypy. Add py38, py39, and nightly (allow to fail)
- In setup.py simplified file and remove Tox and Clean classes
Remove old Python versions (2.7, 3.4, 3.5, and pypy) from Travis
#234: In setup.py simplified file and remove Tox and Clean classes

PR #290: Create semver 3.0.0-alpha0:
- Update README.rst, mention maintenance branch maint/v2.
- Remove old code mainly used for Python2 compatibility, adjusted code to support Python3 features.
- Split test suite into separate files under tests/ directory
- Adjust and update setup.py. Requires Python >=3.6.* Extract metadata directly from source (affects all the __version__, __author__ etc. variables)
#276: Document how to create a sublass from VersionInfo class
#270: Configure Towncrier (PR #273):
- Add changelog.d/.gitignore to keep this directory
- Create changelog.d/README.rst with some descriptions
- Add changelog.d/_template.rst as Towncrier template
- Add [tool.towncrier] section in pyproject.toml
- Add “changelog” target into tox.ini. Use it like tox -e changelog -- CMD whereas CMD is a Towncrier command. The default tox -e changelog calls Towncrier to create a draft of the changelog file and output it to stdout.
- Update documentation and add include a new section “Changelog” included from changelog.d/README.rst.
#213: Add typing information

#291: Disallow negative numbers in VersionInfo arguments for major, minor, and patch.

(in alphabetical order)

Thanks to all! ❤️