Add WebProxySettings (use when proxying requests) (#370)

* webproxy part 1

* fixed

* Push to MyGet

* WebProxy standalone

* -n true

* nuget --- "-n true"

* AllowAutoRedirect

* .

src/WireMock.Net/Compatibility/WebProxy.cs

@@ -0,0 +1,28 @@
+#if NETSTANDARD1_3
+using System;
+using System.Net;
+
+namespace System.Net
+{
+    internal class WebProxy : IWebProxy
+    {
+        private readonly string _proxy;
+        public ICredentials Credentials { get; set; }
+
+        public WebProxy(string proxy)
+        {
+            _proxy = proxy;
+        }
+
+        public Uri GetProxy(Uri destination)
+        {
+            return new Uri(_proxy);
+        }
+
+        public bool IsBypassed(Uri host)
+        {
+            return true;
+        }
+    }
+}
+#endif