play: first stab at 'Redo the onStream ...' for elastic#136

Author: trentm

README.md

@@ -218,9 +218,9 @@ The client is not closed when the `request-error` event is emitted.
 
 ### `client.sent`
 
-An integer indicating the number of events (spans, transactions, or errors)
-sent by the client. An event is considered sent when the HTTP request
-used to transmit it have ended.
+An integer indicating the number of events (spans, transactions, errors, or
+metricsets) sent by the client. An event is considered sent when the HTTP
+request used to transmit it has ended.
 
 ### `client.config(options)`