Keepachangelog-manager

Fixed
- Report an error when using the `release` command without the `[Unreleased]` section being present

Changed
- The `to-json` output is now prettified

Added
- New option `--input-file` for managing CHANGELOG files in a different location

Changed
- The `CHANGELOG.json` file will now consist of an array of releases instead of having each release as dict-key

Fixed
- The `release` command is working correct again

Added
- The command `to-json` allows you to export the changelog contents in JSON format (useful for external automation purposes)

Added
- References to the Homepage and Issue Tracker in the package metadata