title: Revision history with firebase real time database
body: <p>I'm the working on an <a href="https://www.codiva.io" rel="noreferrer">online ide editor for students - codiva.io</a> 
  I'm planning to support collaboration and revision history, i see that firebase real time database would be great fit for this use case.
  Collaboration seems easy, but I couldn't find much info on whether firebase automatically maintains the revision history or if this has to be implemented separately.
  I assume firebase uses diffs to sync between devices and probably use operational transformation for resolving conflicts. 
  Is it possible to capture the diffs and store separately so that I can support a consistent revision history.</p>