title: Converting camel case to underscore case in ruby
body: <p>Is there any ready function which converts camel case Strings into underscore separated string?</p>
  
  <p>I want something like this:</p>
  
  <pre><code>"CamelCaseString".to_underscore      
  </code></pre>
  
  <p>to return "camel_case_string".</p>
  
  <p>...</p>