Post mortems for the jekyll/kramdown footnote "truncation" issue

We ran into an issue where footnotes in the HTML would be cut off in the middle of a sentence, and the cut-off part would be placed elsewhere in the rendered HTML. See b3aae168 for a description of the issue and the workaround to it.

The subsequent commits (245f9bf7 and 3d3d2bc6) fixed two further instances.

Add a monitor job that'll fire if we run into any further instances of this issue (@holger)
Isolate the issue and report a bug to jekyll/kramdown upstream

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