Feature/system.text.json (#192)

Initial support for System.Text.Json and some refactoring

CryptoExchange.Net/Converters/SystemTextJson/SerializerOptions.cs

@@ -0,0 +1,27 @@
+using System.Text.Json;
+using System.Text.Json.Serialization;
+
+namespace CryptoExchange.Net.Converters.SystemTextJson
+{
+    /// <summary>
+    /// Serializer options
+    /// </summary>
+    public static class SerializerOptions
+    {
+        /// <summary>
+        /// Json serializer settings which includes the EnumConverter, DateTimeConverter, BoolConverter and DecimalConverter
+        /// </summary>
+        public static JsonSerializerOptions WithConverters { get; } = new JsonSerializerOptions
+        {
+            NumberHandling = JsonNumberHandling.AllowReadingFromString | JsonNumberHandling.AllowNamedFloatingPointLiterals,
+            PropertyNameCaseInsensitive = false,
+            Converters =
+                    {
+                        new DateTimeConverter(),
+                        new EnumConverter(),
+                        new BoolConverter(),
+                        new DecimalConverter(),
+                    }
+        };
+    }
+}