Add support for recording console output

This commit adds support for recording console output
as well as exporting it to either text or HTML. A user can
also provide their own encoder if they wish.

src/Spectre.Console/Extensions/RecorderExtensions.cs

@@ -0,0 +1,44 @@
+using System;
+using Spectre.Console.Internal;
+
+namespace Spectre.Console
+{
+    /// <summary>
+    /// Contains extension methods for <see cref="Recorder"/>.
+    /// </summary>
+    public static class RecorderExtensions
+    {
+        private static readonly TextEncoder _textEncoder = new TextEncoder();
+        private static readonly HtmlEncoder _htmlEncoder = new HtmlEncoder();
+
+        /// <summary>
+        /// Exports the recorded content as text.
+        /// </summary>
+        /// <param name="recorder">The recorder.</param>
+        /// <returns>The recorded content as text.</returns>
+        public static string ExportText(this Recorder recorder)
+        {
+            if (recorder is null)
+            {
+                throw new ArgumentNullException(nameof(recorder));
+            }
+
+            return recorder.Export(_textEncoder);
+        }
+
+        /// <summary>
+        /// Exports the recorded content as HTML.
+        /// </summary>
+        /// <param name="recorder">The recorder.</param>
+        /// <returns>The recorded content as HTML.</returns>
+        public static string ExportHtml(this Recorder recorder)
+        {
+            if (recorder is null)
+            {
+                throw new ArgumentNullException(nameof(recorder));
+            }
+
+            return recorder.Export(_htmlEncoder);
+        }
+    }
+}