Issue #89: Changed function PositionOpen to use json request/response

MtApi5/Requests/RequestType.cs

@@ -1,13 +1,13 @@
-using System.Diagnostics.CodeAnalysis;
+// ReSharper disable InconsistentNaming
 
 namespace MtApi5.Requests
 {
-    [SuppressMessage("ReSharper", "InconsistentNaming")]
     internal enum RequestType
     {
         Unknown         = 0,
         CopyTicks       = 1,
         iCustom         = 2,
-        OrderSend       = 3
+        OrderSend       = 3,
+        PositionOpen    = 4
     }
 }