C++ tutorial: Remove inline code for the memory tile chapter

docs/tutorial/cpp/src/memory_tile.60

@@ -0,0 +1,26 @@
+/* LICENSE BEGIN
+    This file is part of the SixtyFPS Project -- https://sixtyfps.io
+    Copyright (c) 2020 Olivier Goffart <olivier.goffart@sixtyfps.io>
+    Copyright (c) 2020 Simon Hausmann <simon.hausmann@sixtyfps.io>
+
+    SPDX-License-Identifier: GPL-3.0-only
+    This file is also available under commercial licensing terms.
+    Please contact info@sixtyfps.io for more information.
+LICENSE END */
+// ANCHOR: main_window
+MemoryTile := Rectangle {
+    width: 64px;
+    height: 64px;
+    background: #3960D5;
+
+    Image {
+        source: @image-url("icons/bus.png");
+        width: parent.width;
+        height: parent.height;
+    }
+}
+
+MainWindow := Window {
+    MemoryTile {}
+}
+// ANCHOR_END: main_window

docs/tutorial/cpp/src/memory_tile.md

@@ -10,21 +10,7 @@ mixing values with different units attached to them.
 We copy the following code into the `memory.60` file:
 
 ```60
-MemoryTile := Rectangle {
-    width: 64px;
-    height: 64px;
-    background: #3960D5;
-
-    Image {
-        source: @image-url("icons/bus.png");
-        width: parent.width;
-        height: parent.height;
-    }
-}
-
-MainWindow := Window {
-    MemoryTile {}
-}
+{{#include memory_tile.60:main_window}}
 ```
 
 Inside the <span class="hljs-built_in">Rectangle</span> we place an <span class="hljs-built_in">Image</span> element that