Add the new API Methods Reveal.prevFragment() and Reveal.nextFragment()

Because of consistency with the existent methods Reveal.prev() and Reveal.next()

Might be better to use one variable with different values.

And emit 'fragmentchanged' with the appropriate fragmentData to show or hide fragments.

Making it possible to call the methods Reveal.nextFragment() and Reveal.previousFragment() from »outside«.

Document zooming feature

Reverted to c34be2e9

Using the latest Uglify JS with --no-seqs

Handling the fullscreen functionality via the fullscreen JavaScript API.

Press »f« on the keyboard to enter fullscreen mode.

fixed link for browser support

was pointing at changelog