Add object interface illustration

Author: marijnh

Diff for: 06_object.txt

@@ -35,6 +35,8 @@ _interface_ through which the object is to be used. The idea is that
 the _interface_ is relatively simple, and all the complex things going
 on _inside_ of the object can be ignored when working with it.
 
+image::img/object.jpg[alt="A simple interface can hide a lot of complexity"]
+
 As an example, you can imagine an object that provides an interface to
 an area on your screen. It provides a way to draw shapes or text onto
 this area, but hides all the details of how these shapes are converted

Diff for: html/index.html

@@ -22,8 +22,9 @@ <h1>Eloquent JavaScript<div style="font-size: 70%">second edition</div></h2>
 
   <p>Illustrations by various artists: Sea of bits (chapter 1) and
   weresquirrel (chapter 4) by Margarita Martínez and José Menor.
-  Mysterious computer (introduction) by Philip Tyrer. Octopuses (chapter
-  2 and 4) by Jim Tierney. Regular expression diagrams in chapter 9
+  Mysterious computer (introduction) by Philip Tyrer. Octopuses
+  (chapter 2 and 4) by Jim Tierney. Object with on/off switch (chapter
+  6) by Dyle MacGregor. Regular expression diagrams in chapter 9
   generated with <a href="http://regexper.com">regexper.com</a> by
   Jeff Avallone.</p>