Improve godoc for status codes

Closes #151

frame.go

@@ -203,32 +203,37 @@ type StatusCode int
 
 // These codes were retrieved from:
 // https://www.iana.org/assignments/websocket/websocket.xhtml#close-code-number
+//
+// In addition to the defined constants, 4000-4999 may be used by applications.
 const (
-	StatusNormalClosure StatusCode = 1000 + iota
-	StatusGoingAway
-	StatusProtocolError
-	StatusUnsupportedData
+	StatusNormalClosure   StatusCode = 1000
+	StatusGoingAway       StatusCode = 1001
+	StatusProtocolError   StatusCode = 1002
+	StatusUnsupportedData StatusCode = 1003
 
-	_ // 1004 is reserved.
+	// 1004 is reserved and so not exported.
+	statusReserved StatusCode = 1004
 
-	StatusNoStatusRcvd
+	// StatusNoStatusRcvd cannot be sent as reserved for when
+	// a close message is received without an explicit status.
+	StatusNoStatusRcvd StatusCode = 1005
 
-	// This StatusCode is only exported for use with Wasm.
+	// StatusAbnormalClosure is only exported for use with Wasm.
 	// In non Wasm Go, the returned error will indicate whether the connection was closed or not or what happened.
-	StatusAbnormalClosure
-
-	StatusInvalidFramePayloadData
-	StatusPolicyViolation
-	StatusMessageTooBig
-	StatusMandatoryExtension
-	StatusInternalError
-	StatusServiceRestart
-	StatusTryAgainLater
-	StatusBadGateway
-
-	// This StatusCode is only exported for use with Wasm.
+	StatusAbnormalClosure StatusCode = 1006
+
+	StatusInvalidFramePayloadData StatusCode = 1007
+	StatusPolicyViolation         StatusCode = 1008
+	StatusMessageTooBig           StatusCode = 1009
+	StatusMandatoryExtension      StatusCode = 1010
+	StatusInternalError           StatusCode = 1011
+	StatusServiceRestart          StatusCode = 1012
+	StatusTryAgainLater           StatusCode = 1013
+	StatusBadGateway              StatusCode = 1014
+
+	// StatusTLSHandshake is only exported for use with Wasm.
 	// In non Wasm Go, the returned error will indicate whether there was a TLS handshake failure.
-	StatusTLSHandshake
+	StatusTLSHandshake StatusCode = 1015
 )
 
 // CloseError represents a WebSocket close frame.
@@ -272,7 +277,7 @@ func parseClosePayload(p []byte) (CloseError, error) {
 // and https://tools.ietf.org/html/rfc6455#section-7.4.1
 func validWireCloseCode(code StatusCode) bool {
 	switch code {
-	case 1004, StatusNoStatusRcvd, StatusAbnormalClosure, StatusTLSHandshake:
+	case statusReserved, StatusNoStatusRcvd, StatusAbnormalClosure, StatusTLSHandshake:
 		return false
 	}