text: Title: Make changelog browsable
  Body: Currently Splinter changelog is available in the Sphinx documentation https://github.com/cobrateam/splinter/tree/master/docs/news
  
  However the changelog is not available in the sidebar http://splinter.readthedocs.io/en/latest/ or easily user discoverable.
  
  I recommend adding a Changelog page in the documentation that indexes all individual changelog entries, making them available easily in Sphinx user browsable documentation.
  
  If you have nothing against this I can make a PR.