style(pre-commit): add pre-commit script for js and ruby

There is an installation script for the pre-commit script as well. This checks if your code follows coding standards, based on:

* [rubocop](https://github.com/bbatsov/rubocop)
* [jshint](http://www.jshint.com/)
* no trailing whitespace, no non-ascii filenames

Everyone, try running the install script and see if it installs the pre-commit dependencies and script fine. I only support Mac and Debian (Ubuntu) for now.

Yay