Feature/expose http handlers (#224)

* temp commit

* trying to work out how to expose the http handlers in a decent way..

* pissing about at lunch

* changed to func so you can instanciate object or new it up each time

* docs for dele handlers

* upgraded to sdk 2.1.4

* some validation for consul services

test/Ocelot.UnitTests/Requester/DelegatingHandlerHandlerProviderTests.cs

@@ -0,0 +1,62 @@
+using System;
+using System.Collections.Generic;
+using System.Net.Http;
+using Ocelot.Requester;
+using Shouldly;
+using TestStack.BDDfy;
+using Xunit;
+
+namespace Ocelot.UnitTests.Requester
+{
+    public class DelegatingHandlerHandlerProviderTests
+    {
+        private readonly DelegatingHandlerHandlerProvider _provider;
+        private List<Func<DelegatingHandler>> _handlers;
+
+        public DelegatingHandlerHandlerProviderTests()
+        {
+            _provider = new DelegatingHandlerHandlerProvider();
+        }
+
+        [Fact]
+        public void should_return_empty_list()
+        {
+            this.When(x => WhenIGet())
+                .Then(x => ThenAnEmptyListIsReturned())
+                .BDDfy();
+        }
+
+        [Fact]
+        public void should_get_delegating_handlers_in_order_first_in_first_out()
+        {   
+            this.Given(x => GivenTheHandlers())
+                .When(x => WhenIGet())
+                .Then(x => ThenTheHandlersAreReturnedInOrder())
+                .BDDfy();
+        }
+
+        private void ThenAnEmptyListIsReturned()
+        {
+            _handlers.Count.ShouldBe(0);
+        }
+
+        private void ThenTheHandlersAreReturnedInOrder()
+        {
+             var handler = (FakeDelegatingHandler)_handlers[0].Invoke();
+            handler.Order.ShouldBe(0);
+            handler = (FakeDelegatingHandler)_handlers[1].Invoke();
+            handler.Order.ShouldBe(1);
+        }
+
+        private void WhenIGet()
+        {
+            _handlers = _provider.Get();
+        }
+
+        private void GivenTheHandlers()
+        {
+            _provider.Add(() => new FakeDelegatingHandler(0));
+            _provider.Add(() => new FakeDelegatingHandler(1));
+        }
+    }
+}