Fossil SCM

As Tcl development moves to adopt more of a fossil-based workflow, we're experimenting with no longer maintaining a separate ChangeLog file. This is mostly OK, but one issue is that where we have a change that is a potential incompatibility, which we would have previously highlighted so that we can explicitly warn people about it in our release notes, it now tends to get lost in the list of commits.

What we would like would be some way to make a tag (e.g., “potential incompatibility”) have some kind of extra visual indication associated with it so that when browsing the timeline, people (and especially our release engineer!) can spot at a glance that something has happened that has a potential impact on downstream programmers. Mere background color doesn't work too well, alas, especially when a lot of different branches are being committed to in quick succession, and getting the history of those commits with that tag directly is currently somewhat uninformative as (usually) there's no timeline-context with the other commits around. Since I'm only looking for a tweak to rendering based off the existing data model, it shouldn't involve too much work. I hope. :-)

If it were possible to (ab)use the mechanism for other things (e.g., flagging major feature additions) that would be cool, but that's a much less important thing. (It could even be something that is configured on a per-repository basis; that would be quite sufficient for our use-case.) But we'd rather not do it through editing the commit comment to wedge more HTML fanciness in there; there's quite enough going on in that poor field right now.

Suggested implementation in [13ba9a50df]. For Tcl it works when adding the following CSS (example: red line around it):

/* the format for the timeline entry with "Potential Incompatibility" */
tr.potential td.timelineTableCell {
  padding: .1em .2em;
  border: 2px solid #ff0000;
}

Handling of multiple tags is not correct yet.