lowdown: update to 0.11.2.

Version 0.11.2, 2022-03-27

Support native roff escapes instead of using Unicode escapes. (This is a
work in progress, as there are many.) This makes special characters usable
in sections and so on.

Fix a bogus free when running lowdown-diff(1). While here, handle differences
between totally-different files, where before we would error out.

Document how differences are displayed in each output mode, as well as how
metadata is a special case. Fix -tterm ANSI escape filtering for background
colour, allowing changes to be viewed again.

Fix a sneaky -tterm bug found by AFL where having the number of footnotes
change digit length (e.g., 9 to 10) within a table would cause an assertion.

Another big thanks to Michael Dexter in providing hardware for continuously
running AFL and finding some of these corner case bugs!

(fcambus)