Handlebars Extension (#286)

* wip

* HandlebarsRegistrationCallback

* HandlebarsContextFactoryTests

* 1.0.21.0

* fix sonar

* LocalFileSystemHandler

* readme

* Fix System.IO.IOException

test/WireMock.Net.Tests/Transformers/HandlebarsContextFactoryTests.cs

@@ -0,0 +1,52 @@
+using FluentAssertions;
+using HandlebarsDotNet;
+using Moq;
+using System;
+using WireMock.Handlers;
+using WireMock.Transformers;
+using Xunit;
+
+namespace WireMock.Net.Tests.Transformers
+{
+    public class HandlebarsContextFactoryTests
+    {
+        private readonly Mock<IFileSystemHandler> _fileSystemHandlerMock = new Mock<IFileSystemHandler>();
+
+        [Fact]
+        public void Create_WithNullAction_DoesNotInvokeAction()
+        {
+            // Arrange
+            var sut = new HandlebarsContextFactory(_fileSystemHandlerMock.Object, null);
+
+            // Act
+            var result = sut.Create();
+
+            // Assert
+            result.Should().NotBeNull();
+        }
+
+        [Fact]
+        public void Create_WithAction_InvokesAction()
+        {
+            // Arrange
+            int num = 0;
+            Action<IHandlebars, IFileSystemHandler> action = (ctx, fs) =>
+            {
+                ctx.Should().NotBeNull();
+                fs.Should().NotBeNull();
+
+                num++;
+            };
+            var sut = new HandlebarsContextFactory(_fileSystemHandlerMock.Object, action);
+
+            // Act
+            var result = sut.Create();
+
+            // Assert
+            result.Should().NotBeNull();
+
+            // Verify
+            num.Should().Be(1);
+        }
+    }
+}