Semversioner

- patch: move main logic into __main__.py

- patch: Include CHANGELOG.md into package.

- patch: Bump jinja2 from 3.1.3 to 3.1.4 to patch CVE-2024-34064.

- patch: Bump jinja2 from 3.1.2 to 3.1.3 to fix CVE-2024-22195.

- patch: Add documentation for custom attributes in the changelog template.

- major: Drop support for Python 3.6 and 3.7 as they are not maintained. Minimum supported version is Python 3.8.
- major: Upgrade project third-party dependencies to latest version.
- minor: Add support for custom properties in changeset files.
- minor: Change deletion logic in `next-release` folder: only delete json files, and delete the folder only if empty. This will allow to keep the `next-release` folder if it contains other files such as `.gitkeep` for example.
- minor: Change json mapper to use granurality of seconds instead of milliseconds for `created_at` field in releases.
- patch: Clean up README Markdown syntax.