handlers must be run once

so remove all occurences of each host from the handlers notified by
lists
Links are the best kinds of instructions

Link people right to this page on Github, so they can click "edit" right there. No need for them to search for the repo, figure out that the docsite isn't a separate repo, and navigate to the given dir.
Nit fix spelling of separate
Merge pull request #2737 from jkleckner/more-spelling

Nit fix spelling of separate
Allow play tagging in context of new meta-tasks.
Merge pull request #2734 from chadoh/patch-2

Documentation: Links are the best kinds of instructions
Merge pull request #2731 from stoned/flush_handlers-cleanup

handlers must be run once
Empty plays should still gather facts