Provide ability to generate 301,307 redirects, or 204 No Content response codes

[cameronjacobson]

This will be useful for things like seamless migration of active clients from one server to another.

Per the spec:
Event stream requests can be redirected using HTTP 301 and 307 redirects as with normal HTTP requests. Clients will reconnect if the connection is closed; a client can be told to stop reconnecting using the HTTP 204 No Content response code