Handlebars Extension (#286)

* wip

* HandlebarsRegistrationCallback

* HandlebarsContextFactoryTests

* 1.0.21.0

* fix sonar

* LocalFileSystemHandler

* readme

* Fix System.IO.IOException

src/WireMock.Net/Transformers/HandlebarsContextFactory.cs

@@ -0,0 +1,34 @@
+using HandlebarsDotNet;
+using System;
+using WireMock.Handlers;
+
+namespace WireMock.Transformers
+{
+    internal class HandlebarsContextFactory : IHandlebarsContextFactory
+    {
+        private static readonly HandlebarsConfiguration HandlebarsConfiguration = new HandlebarsConfiguration
+        {
+            UnresolvedBindingFormatter = "{0}"
+        };
+
+        private readonly IFileSystemHandler _fileSystemHandler;
+        private readonly Action<IHandlebars, IFileSystemHandler> _action;
+
+        public HandlebarsContextFactory(IFileSystemHandler fileSystemHandler, Action<IHandlebars, IFileSystemHandler> action)
+        {
+            _fileSystemHandler = fileSystemHandler;
+            _action = action;
+        }
+
+        public IHandlebars Create()
+        {
+            var handlebarsContext = Handlebars.Create(HandlebarsConfiguration);
+
+            HandlebarsHelpers.Register(handlebarsContext, _fileSystemHandler);
+
+            _action?.Invoke(handlebarsContext, _fileSystemHandler);
+
+            return handlebarsContext;
+        }
+    }
+}