r/t/tag.tmpl: Fix "empty <ul>" tag

When tags are emitted with no "extra", replace the "<ul>" supposed to
contain that "extra" with a "<br />".  This avoids generating invalid
XHTML, which mandates at least one "<li>" member.

Signed-off-by: Niels Thykier <niels@thykier.net>
r/t/{index,tag}.tmpl: Move a <div> outside <p>

According to XHTML strict, <div> tags are not allowed inside a <p>
tag.

Signed-off-by: Niels Thykier <niels@thykier.net>