Git SHAs: Markdown rendering including MRs additional commits
The Markdown rendering subsystem of GitLab is able to link automatically to Git commits.
While doing so, it normalizes the link text to the preferred form, so that, e.g,
ca1234fe56789de01234 becomes just
ca1234fe56. We could take advantage of that to display the Mercurial short node id (truncated hash) instead of the Git commit short id.
This would still not allow people to directly link to Mercurial changesets, but it would immediately apply to "system notes", for instance the additional commits messages in Merge Requests.
Part of #6