0.9.10 release

* Fresh coat of paint on the presenter view. This uses the CSS3 flexbox
  model, so it's much cleaner and will allow more UI work in the future.
* Slide menu in the presenter view now follows the current slide.
* Audience questions can now be dismissed by clicking on them.
* Smartphone remote view simplified, now with hamburger menu button.
* Enables more Markdown extensions as documented in AUTHORING.rdoc