This is orthogonal to behaviour for rendering paths from the beginning of time for branches created
before the first commit, and helps frame the history in a better way.
This further simplifies handling of merges, which was made correct in commit 675e79c. We now
correctly set both source and destination commit references, where an empty source reference means
the base of the branch being merged into.
The primary branch (`master` or whichever other branch is the primary) has now
an automatic merge path that leads to the beginning of time, much like branches
that have been created before the first commit.
The font pitch is also fixed to half the height, as is usually the case with
monospace fonts.