Add support for HandleBars File (to read a file) (#278)

* HandleBarsFileFragment

* 1.0.17

* {{File}}

src/WireMock.Net/Handlers/IFileSystemHandler.cs

@@ -49,12 +49,19 @@ namespace WireMock.Handlers
         void WriteMappingFile([NotNull] string path, [NotNull] string text);
 
         /// <summary>
-        /// Read a response body file as text.
+        /// Read a response body file as byte[].
         /// </summary>
         /// <param name="path">The path or filename from the file to read.</param>
         /// <returns>The file content as bytes.</returns>
         byte[] ReadResponseBodyAsFile([NotNull] string path);
 
+        /// <summary>
+        /// Read a response body file as text.
+        /// </summary>
+        /// <param name="path">The path or filename from the file to read.</param>
+        /// <returns>The file content as text.</returns>
+        string ReadResponseBodyAsString([NotNull] string path);
+
         /// <summary>
         /// Delete a file.
         /// </summary>

src/WireMock.Net/Handlers/LocalFileSystemHandler.cs

@@ -68,6 +68,16 @@ namespace WireMock.Handlers
             return File.ReadAllBytes(Path.GetFileName(path) == path ? Path.Combine(GetMappingFolder(), path) : path);
         }
 
+        /// <inheritdoc cref="IFileSystemHandler.ReadResponseBodyAsString"/>
+        public string ReadResponseBodyAsString(string path)
+        {
+            Check.NotNullOrEmpty(path, nameof(path));
+
+            // In case the path is a filename, the path will be adjusted to the MappingFolder.
+            // Else the path will just be as-is.
+            return File.ReadAllText(Path.GetFileName(path) == path ? Path.Combine(GetMappingFolder(), path) : path);
+        }
+
         /// <inheritdoc cref="IFileSystemHandler.FileExists"/>
         public bool FileExists(string filename)
         {