essessey v0.1.0 — one event model, many deliveries

First release. One Event (a name plus a JSON payload) delivered over SSE, NATS
or WebSocket, with the payload identical across all three.

SSE is treated as a FORMAT rather than a transport peer: it frames because an
HTTP body is an undelimited stream, while message-oriented bindings carry the
payload unframed. Zero transport dependencies -- the NATS and WebSocket
bindings take the minimal interface each needs from a caller-supplied client.

elelemstream bridges elelem's callbacks to the block protocol, owning the
block-index arithmetic, and is the only subpackage that imports elelem.