Change module system of the main file

[thiamsantos]

I tried to make less changes as possible, but to solve #92 I needed to add a build process. So, if this PR be accepted, all future changes needed to be done on the file index.es.js which will compiled to index.js running npm run build.

Changelog:

• Added rollup to compile the module.
• Changed jshint/jscs config to make the tests pass.
• Expose a version using es6 modules on module and jsnext:main properties of package.json.

[thiamsantos]

Thanks @flitbit!!!! Are you going to release these changes soon?

[flitbit]

Working on rollup release right now.