This module provides a simple API for publishing messages to channels
and for subscribing to them.

When a message is published on a channel, all subscribers currently in
that channel will get it on their next "get" or "get_all" call.

Currently, it offers three backends: "DBM_Deep" for on-disk storage,
"Memcached" for possibly multi-host storage, and "PlainHash" for
single-process storage.