Vacation extension: added min/max period configuration settings and changed the internal unit from days to seconds.

Improved ManageSieve config example; 'sieve' is added to protocols setting in 20-managesieve.conf now.

- No longer track the generated pigeonhole.7
- Some makes don't like the 'handy' notation that was used.
- Deleted trailing spaces
- Escaped some dashes
- Replaced some ' and " by \(aq and \(dq
- Sorted manual pages in section 'See also'
  (first list all man pages from the lowest section (1)
  alphabetical sorted, then the next section …)