add changelog

[line-o]

The changelog should be created from the information gathered for the release notes.

The release automation should also generate / append the changelog with the (formatted) release notes from semantic-release (see https://github.com/semantic-release/changelog).

The file must be in a format that the public package repository supports so that it is visible on the roaster package information page

[line-o]

Public repo does support adding them as XML into repo.xml.

• Add changelog-element to repo.xml
• for each released version there should be one change-element with a version-attribute
• each change has an unordered list (in xhtml namespace)

    <changelog>
        <change version="5.0.2">
            <ul xmlns="http://www.w3.org/1999/xhtml">
                <li>Enhanced docx to TEI import</li>
                <li>Fix whitespace issues around pb-popover</li>
                <li>Fixed login issue if user belongs to multiple groups</li>
            </ul>
        </change>
    ...
   </changelog>

The plugin does produce a changelog.md by default. It is unclear if this file and format can be used directly. It would simplify the process a great deal if it did.

[line-o]

I just checked the current implementation of the public package repository. It can only read changelogs in repo.xml