The URLs of the form `help://man/<section>/<page>` link to another help
page inside the help application. All previous relative page links are
replaced by this new form. This doesn't change any behavior but it looks
much nicer :^)
Note that man doesn't handle these new links, but the previous relative
links didn't work either.
A quick grep revealed these stats (counting only the first occurrence
per line):
`thing`(1): 154
`thing(1)`: 9
thing(1): 4
This commit converts all occurrences to the `thing`(1) format.
