Cleanup some manpages:

- All man pages: fix those which use ".It" for an item, but to not                                                              se items; use ".It Ev" instead.

- pkg-fetch.8: Fix up some layout/formatting via use of ".Pp",
  and mention fetch(3) in SEE ALSO.

- pkg.8: Mention SBUF(9), elf(3), fetch(3), libarchive(3), and
  pthread(3) in SEE ALSO.  (I don't know how to mention libutil,
  since there is no universal man page for it)

- pkg.conf.5: Mention fetch(3) in SEE ALS