Multiple authors are not represented in the changelog

**What happened**:
A number of scenarios results in multiple authors:
* Multiple PRs to fix an issue from different authors
* Multiple pushes from different authors to the same PR, Github attributes the additional contributors as co-authors

**What you expected to happen**:
All authors to be included in the changelog

Begin by tracing Chronicle’s GitHub pull-request author handling and changelog assembly. Check how multiple PR authors and co-authors are represented, then verify the result against both scenarios described in the issue; done means every contributing author appears in the generated changelog.

Written by the indexing model from the issue text.