Add countenvelope encoder with marshal/unmarshal support, buffer pool integration, and tests; improve error messages for subscription validation

pkg/encoders/event/event.go

@@ -297,7 +297,7 @@ InVal:
 		}
 		if len(id) != sha256.Size {
 			err = errorf.E(
-				"invalid ID, require %d got %d", sha256.Size,
+				"invalid Subscription, require %d got %d", sha256.Size,
 				len(id),
 			)
 			return

pkg/encoders/event/signatures.go

@@ -34,13 +34,13 @@ func (ev *E) Verify() (valid bool, err error) {
 		// check that this isn't because of a bogus ID
 		id := ev.GetIDBytes()
 		if !utils.FastEqual(id, ev.ID) {
-			log.E.Ln("event ID incorrect")
+			log.E.Ln("event Subscription incorrect")
 			ev.ID = id
 			err = nil
 			if valid, err = keys.Verify(ev.ID, ev.Sig); chk.E(err) {
 				return
 			}
-			err = errorf.W("event ID incorrect but signature is valid on correct ID")
+			err = errorf.W("event Subscription incorrect but signature is valid on correct Subscription")
 		}
 		return
 	}