purge old zensu files

If these need to come back, they'll be resurrected.
reorganize client/server

Move all files into root, discarding the concept of server and client

Rename FailureDetector to Node, to encapsulate all information about a
remote node. Node now contains its own (non-actor) fd.

create a local Node accessible at Zensu.node
move Broadcaster and Subscribr to examples directory

They are really just wrappers around RemoteNotifier. Not needed yet.
add Stethoscope.add_node
call config callbacks on creation if key exists

If the key is already set, the callback won't get called because it
missed the initial broadcast. In most cases the callback should be
manually called with the current value. Pass the initial_set: false to
avoid this.

This is only enabled for callbacks that subscribe to a specific key and the
:set action.
attach fsm to Actor.current instead of self

self might work, but Actor.current is more correct according to the
Gotchas page on the celluloid wiki.
override Node#inspect to avoid stack overflow issues

Might be an issue with FSM?
use a mutex to synchronize access to config
publish config changes asynchronously
add basic Router and Message

Router is similar to the PubsubNotifier, but using the semantics of a
router socket.

Message is a versioned message container with headers.
add id to Message
restrict compile_methods! to valid method keys

Actually a little more restrictive than that to avoid potential issues.
extract most of Configuration to Registry

A Registry is a Hash that publishes updates to itself. A configuration
is a Registry with method access to keys.
add a nodes registry at Zensu.nodes

This stores the list of known Nodes. Might move somewhere else.
note about compiling writer methods too
attempt to fix default_registry
remove the default_registry

It wasn't useful and complicated the code
only fire callbacks with matching registry topics
Reference registries by id instead of topic
subscribe before initial_set

There is a race condition between the initial_set and subscribe. With
the set first, you risk losing updates. With the subscribe first, you
risk having callbacks fire twice.

Callbacks firing twice is better than not at all, so the subscribe is
first. However this means callbacks should be idempotent.