"data" in this example will be notifyasync (i.e., the SingleAsyncWork object whose handle was sent to uv_async_send); might be nicer to call it "work". No idea what "status" is.
Would be good to document this in the manual (it only says "you'll most likely just discard" the callback parameters). In the case of ZMQ, I actually use the "data" parameter (https://github.com/JuliaLang/ZMQ.jl/blob/master/src/ZMQ.jl#L316-L334).
