Links to a specific doc page have to point to the .h page, not the .html
one.
See https://github.com/hotdoc/hotdoc/issues/81

 for details.

Signed-off-by: Guillaume Desmottes <guillaume.desmottes@collabora.co.uk>
Reviewed-by: Mathieu Duponchelle <mathieu.duponchelle@collabora.co.uk>
Differential Revision: https://phabricator.apertis.org/D5383