Support Type_Notification and report on them.
Don't automatically read config from an XML file.

This can cause confusion if you've happened to enable saveconfig but
then want to test something else.  If it proves useful for anything then
we can add it back later as part of a config option.
Add .enablePoll() and .disablePoll().

Indiscriminately polling everything we find didn't work so well, I guess
some values just don't like it.  Leave it to the user to poll values
that they care about, giving an example of binary and multi-level
switches to start with.

We need to revisit this at some point to correctly log whether a value
is being polled or not.

Update docs.
Ignore NodeNew, fix znodes creation.

We weren't actually getting these messages, and so we were never adding
to the znodes list.  Key off NodeAdded instead, which does fire, and we
can revisit NodeNew later to see if it can be used for anything useful.