add new method engineDidOpen in socketEngineClient protocol

Source/SocketEngine.swift

@@ -762,6 +762,7 @@ extension SocketEngine {
             connected = true
             probing = false
             polling = false
+            client?.engineDidOpen!("Connect")
         }
     }
     

Source/SocketEngineClient.swift

@@ -30,4 +30,5 @@ import Foundation
     func engineDidClose(reason: String)
     func parseEngineMessage(msg: String)
     func parseEngineBinaryData(data: NSData)
+    optional func engineDidOpen(reason: String)
 }