Update .npmignore.

* Fix ignoring doc/ folder
* Add CONTRIBUTING.md
Quote node.js version in .travis.yml.

This way, the exact version will be used instead of 0.1.
Update all dependencies to their latest versions.
Normalize package.json.
Update .jshintrc.

Specify `indent` and `trailing` options.
Bump npm version.

The version now specified is the one the latest node.js ships with. This avoids a warning when doing `npm install`. Not sure if `npm` is worth being specified at all here.
README.md: Add dependency badges.
Explicitly specify the files to install.

Instead of specifying the files to ignore, do the opposite.
Update code for the new Clean-css.
Merge pull request #37 from XhmikosR/master

Minor tweaks