Network client for connecting to a Riemann server. Usage:

(def c (tcp-client {:host "monitoring.local"}))

(send-event c {:service "fridge"
               :state "running"
               :metric 2.0
               :tags ["joke"]})
=> #<com.riemann.riemann.client.MapPromise ...>

@(query c "tagged \"joke\"")
=> [{:service "fridge" ... }]

(close! c)

Clients are resistant to failure; they will attempt to reconnect a dropped
connection periodically. Note that clients will not automatically queue or
retry failed sends.

Encodes and decodes Riemann messages and events, between byte arrays,
buffers, and in-memory types.