[Modify] Add it

websocket-sharp/Net/HttpUtility.cs

@@ -393,6 +393,12 @@ namespace WebSocketSharp.Net
       _entities.Add ("euro", '\u20AC');
     }
 
+    private static bool isAlphabet (char c)
+    {
+      return (c >= 'A' && c <= 'Z')
+             || (c >= 'a' && c <= 'z');
+    }
+
     private static bool isNumeric (char c)
     {
       return c >= '0' && c <= '9';