title: Use Range data type in Mongoid
body: <p>I am using Mongoid (4.0.0.alpha2) with rails-api (<a href="https://github.com/rails-api/rails-api" rel="nofollow">https://github.com/rails-api/rails-api</a>).</p>
  
  <p>I am looking for example on usage of "Range" (<a href="http://mongoid.org/en/mongoid/docs/documents.html#fields" rel="nofollow">http://mongoid.org/en/mongoid/docs/documents.html#fields</a>) as datatype in my model.</p>
  
  <p>Can I create an index on a field with datatype "Range"?</p>
  
  <p>Thanks</p>