Various fixes

Requests/Request.cs

@@ -1,5 +1,7 @@
 using System;
+using System.IO;
 using System.Net;
+using System.Threading.Tasks;
 using CryptoExchange.Net.Interfaces;
 
 namespace CryptoExchange.Net.Requests
@@ -18,11 +20,30 @@ namespace CryptoExchange.Net.Requests
             get => request.Headers;
             set => request.Headers = value;
         }
+        public string ContentType
+        {
+            get => request.ContentType;
+            set => request.ContentType = value;
+        }
+
+        public string Accept
+        {
+            get => ((HttpWebRequest)request).Accept;
+            set => ((HttpWebRequest)request).Accept = value;
+        }
+
+        public long ContentLength
+        {
+            get => ((HttpWebRequest)request).ContentLength;
+            set => ((HttpWebRequest)request).ContentLength = value;
+        }
+
         public string Method
         {
             get => request.Method;
             set => request.Method = value;
         }
+
         public Uri Uri => request.RequestUri;
 
         public void SetProxy(string host, int port)
@@ -30,9 +51,14 @@ namespace CryptoExchange.Net.Requests
             request.Proxy = new WebProxy(host, port);
         }
 
-        public IResponse GetResponse()
+        public async Task<Stream> GetRequestStream()
         {
-            return new Response(request.GetResponse());
+            return await request.GetRequestStreamAsync();
+        }
+
+        public async Task<IResponse> GetResponse()
+        {
+            return new Response(await request.GetResponseAsync().ConfigureAwait(false));
         }
     }
 }