title: Joda Time get Duration between two Instants
body: <p>I have two <code>Instant</code> objects and would like to get a <code>Duration</code> indicating how much time is between them, however <code>Instant.minus</code> only accepts either a <code>ReadableDuration</code> or a <code>long</code> for the amount of time to change by, and doesn't seem to have any method for subtracting two instants to get the difference between them.</p>
  
  <p>Other answers that I found seem to suggest converting both instants to milliseconds and doing the math myself, but I would prefer something that retains type safety and doesn't require re-implementing end - start logic.</p>
  
  <p>How can I get a <code>Duration</code> from two <code>Instant</code>s?</p>