Closes #1226, #1538.

The `reveal.js` npm module is typically installed to access the CSS/JS
assets for Reveal.js. For those that want to run the plugins, they would
clone the whole repository. Hence, it doesn’t make sense to include
those as `dependencies`, which will increase download times.

Closes #1734.

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.

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.

* 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

-allows security vulnerability check in used npm-dependencies and own scripts
-execute with ```grunt retire```

prevents XSS vulnerability (see https://github.com/janl/mustache.js/pull/388)

the `licenses` field in package.json is deprecated. https://docs.npmjs.com/files/package.json#license

The `license` field is the recommended field and expects an SPDX expression.

Right now the package is not recognized as usable library by Browserify.
Adding the main attribute in the package.json solves that, and now gives
others the possibility to use reveal as a library in more complex
systems.

re-created unprefixed version of reveal.css automatically using autoprefixer, to facilitate merging of changes to it