Optional change types

[tomwyr]

Currently, it is not possible to use the library to query change logs that omit change types, e.g.:

This does work:

## 1.0.0 - 2025-10-30

### Added

- Change with type

// log.get('1.0.0').changes() => [Change with type]

While this doesn't:

## 1.0.0 - 2025-10-30

- Change without type

// log.get('1.0.0').changes() => []

In projects where the number of changes between versions is low or the project simply doesn't group changes by type, it'd make the library usable, if it parsed ungrouped change nodes.