Closes #1163, #1495.

Reduce required Node.js version to 4.0.0.

The development workflow can be used with Node 4+, not just Node 6. We
should avoid showing warnings and errors when users are installing this
package via npm/yarn.

Ref. #1729, #1743.
Closes #1725.

Hide slide number when in paper or pdf print view

Bump node engine in packages.json

Defaults in README are not current

include contributors in (c)

Implementing a better data-trim

* Allow slides to be served away from revealjs server location

The previous 'base' option conflicts with Grunt's 'base' option.
Changing it to 'root' avoids this. Further, updating to a newer Grunt
allows multiple parameters to be used. therefore `grunt serve --root="."
--root="pathtomyslides"` allows you to keep your slide content separate
from JS/CSS and such

* Live reload for relocated base

* Updated packages to match origin/dev

* Updated packages to match origin/dev

* Ensure root is an array

fix #1607

The autoSlide duration of media elements with data-autoplay now takes the playbackRate of said media element into account when setting the duration so that autoSlide and the media element stay in sync.

On Ubuntu 16.04, the Logitech R400's blackout button gets mapped to 'v'
(keyCode 86). I don't know why this is, but since nothing else is
currently using 'v', this allows it to be supported out of the box.