title: How do you get category info of a book from ISBNdb.com?
body: <p>I am able to easily get book info:</p>
  
  <pre><code>http://isbndb.com/api/books.xml?access_key=THEKEY&amp;results=details&amp;index1=isbn&amp;value1=9781849152990
  </code></pre>
  
  <p>And I can easily look up categories:</p>
  
  <pre><code>http://isbndb.com/api/categories.xml?access_key=Z&amp;index1=category_id&amp;value1=science.mathematics.geometry 
  </code></pre>
  
  <p>But how do you get a certain book's category? I want to provide the ISBN code, and in return I want to get the category?</p>