Merge pull request #394 from hintjens/master

Tweaked _dup and _print
zloop: interpret a pollitem with socket=NULL and fd=0 as 'poll on fd 0'
Merge pull request #395 from mhaberler/master

zloop: interpret a pollitem with socket=NULL and fd=0 as 'poll on fd 0'
Updated man page
Removed experimental zservice class