title: Parse Date string in Ruby
body: <p>I have a String <code>20120119</code> which represents a date in the format <code>'YYYYMMDD'</code>.</p>
  
  <p>I want to parse this string into a Ruby object that represents a Date so that I can do some basic date calculation, such as diff against today's date.</p>
  
  <p>I am using version 1.8.6 (requirement).</p>