The \f(CW macro to switch to "constant-width" does not seem to
honored when converting to html, and I've found some patch to
groff removing its use from their own man page.
https://lists.gnu.org/archive/html/groff-commit/2020-07/msg00015.html
Lets use \fC instead, as it seems to produce some <tt> in HTML.
Two manpages had URLs pointing to spot.lrde.epita.fr instead of
spot.lre.epita.fr.
Finally, spot-x.x had an incorrectly closed .EX block, that completly
broke the HTML conversion.
* bin/man/autcross.x, bin/man/ltl2tgba.x, bin/man/ltlcross.x,
bin/man/spot-x.x, bin/man/spot.x: Fix the aforementioned issues.
