Going ES6

[mkxml]

I've been thinking recently that making a switch over to pure JS (EcmaScript 6) would be a better choice to help contributors get used with the codebase.

The idea is to keep the current API and port the CoffeeScript code over to ES6.

To make that possible we would need to use the popular tool called babel since ES6 support is not yet complete in the majority of the browsers we want to support.

It's important to cover this issues:

• [x] It must be done in a specific branch and only merged when ready.
• [ ] It must maintain the existent API, thus people using it right now won't notice the change when updating.
• [ ] A styleguide should be used as base, Airbnb's JavaScript Guide is a great choice.
• [ ] The test suite should be written using JS.
• [ ] Document the code with jsdoc, most annotations can be easily ported from the currently used codo format.
• [ ] The test process should remain the same.
• [ ] The high level exposed grunt tasks should remain the same.

[mkxml]

Created es6-refactor branch for work related to this issue.