add json dispatcher.

src/DotNetCore.CAP/Dashboard/JsonDispatcher.cs

+using System;
+using System.Net;
+using System.Threading.Tasks;
+using Newtonsoft.Json;
+using Newtonsoft.Json.Converters;
+using Newtonsoft.Json.Serialization;
+
+namespace DotNetCore.CAP.Dashboard
+{
+    internal class JsonDispatcher : IDashboardDispatcher
+    {
+        private readonly Func<DashboardContext, object> _command;
+
+        public JsonDispatcher(Func<DashboardContext, object> command)
+        {
+            _command = command;
+        }
+
+        public async Task Dispatch(DashboardContext context)
+        {
+            var request = context.Request;
+            var response = context.Response;
+
+            object result = _command(context);
+            
+            var settings = new JsonSerializerSettings
+            {
+                ContractResolver = new CamelCasePropertyNamesContractResolver(),
+                Converters = new JsonConverter[] { new StringEnumConverter { CamelCaseText = true } }
+            };
+            var serialized = JsonConvert.SerializeObject(result, settings);
+
+            context.Response.ContentType = "application/json";
+            await context.Response.WriteAsync(serialized);
+        }
+    }
+}