doc: fixed the Synopsis a bit.
bugfix: get_servers(): we did not take into account multiple peers in a single server (from domains resolved to multiple IP addresses).
feature: added new method get_peers().
renamed the get_peers() method to get_primary_peers(). also added more docs.
feature: added new method get_backup_peers().
doc: formatting fixes.
doc: minor fixes.
feature: added an "id" field to the records returned by get_primary_peers() and get_backup_peers().
doc: minor formatting fixes.
massive code refactoring.
feature: added set_peer_down method to turn on and off a specified peer.
doc: added a note regarding synchronizing changes across all the nginx workers.
doc: mentioned the lua-resty-upstream-healthcheck library that makes use of this module.