Issue #31: Implemented function SymbolInfoDouble in MtApi MT4

MtApi/Requests/RequestType.cs

@@ -13,6 +13,7 @@
         iCustom             = 8,
         CopyRates           = 9,
         Session             = 10,
-        SeriesInfoInteger   = 11
+        SeriesInfoInteger   = 11,
+        SymbolInfoDouble    = 12
     }
 }

MtApi/Requests/SymbolInfoDoubleRequest.cs

@@ -0,0 +1,12 @@
+using System;
+
+namespace MtApi.Requests
+{
+    internal class SymbolInfoDoubleRequest : RequestBase
+    {
+        public override RequestType RequestType => RequestType.SymbolInfoDouble;
+
+        public string SymbolName { get; set; }
+        public int PropId { get; set; }
+    }
+}