title: Get difference between DateTime instances with clj-time
body: <p>I am trying to calculate the difference between two DateTime instances using <a href="https://github.com/clj-time/clj-time" rel="noreferrer">clj-time</a>. I looked through the documentation and found <code>clj-time.core/minus</code> and <code>clj-time.core/minus-</code> but both require an instance of <code>org.joda.time.ReadablePeriod</code> and not one of <code>DateTime</code>. I would prefer to use cli-time, but if no solution exists, what would be the cleanest method of calculating the delta using Joda Time?  </p>
  
  <p>Thank you for the help.</p>