Issue #100: implemented second function SymbolInfoString (MT5)

MtApi5/Requests/RequestType.cs

@@ -4,13 +4,14 @@ namespace MtApi5.Requests
 {
     internal enum RequestType
     {
-        Unknown         = 0,
-        CopyTicks       = 1,
-        iCustom         = 2,
-        OrderSend       = 3,
-        PositionOpen    = 4,
-        OrderCheck      = 5,
-        MarketBookGet   = 6,
-        IndicatorCreate = 7
+        Unknown             = 0,
+        CopyTicks           = 1,
+        iCustom             = 2,
+        OrderSend           = 3,
+        PositionOpen        = 4,
+        OrderCheck          = 5,
+        MarketBookGet       = 6,
+        IndicatorCreate     = 7,
+        SymbolInfoString    = 8
     }
 }

MtApi5/Requests/SymbolInfoStringRequest.cs

@@ -0,0 +1,10 @@
+namespace MtApi5.Requests
+{
+    internal class SymbolInfoStringRequest : RequestBase
+    {
+        public override RequestType RequestType => RequestType.SymbolInfoString;
+
+        public string SymbolName { get; set; }
+        public ENUM_SYMBOL_INFO_STRING PropId { get; set; }
+    }
+}

MtApi5/Requests/SymbolInfoStringResult.cs

@@ -0,0 +1,8 @@
+namespace MtApi5.Requests
+{
+    internal class SymbolInfoStringResult
+    {
+        public bool RetVal { get; set; }
+        public string StringVar { get; set; }
+    }
+}