title: get the ASIN number from amazon URL
body: <p>Given a amazon product URL, which can either be </p>
  
  <pre><code>http://amazon.com/gp/product/ASIN/*
  http://amazon.com/*/dp/ASIN/*
  http://amazon.com/dp/ASIN/*
  </code></pre>
  
  <p>how do i scrap the ASIN number from the URL in Ruby ? I am not good at writing regular expressions.</p>