title: Delete by Id in mongoid
body: <p>Is there any one command in Mongoid to delete an object using id?</p>
  
  <p>Something like,</p>
  
  <pre><code>ClassName.delete(:id)
  </code></pre>
  
  <p>Currently i dont see anything like that and im using,</p>
  
  <pre><code>obj = ClassName.find(:id)
  obj.delete
  </code></pre>
  
  <p>Can it be any better?</p>