Coffee -> ES6

[florrain]

Overview

This PR is bundling a bunch of things that I wanted to apply on the repo to make it a little more up-to-date, and hopefully easier to work with:

• Translation of CoffeeScript files to Javascript ES6
• Update of the build pipeline to Gulp/Babel
• Linting with ESLint + AirBnb codestyle
• A dev task (as default when running gulp) to watch, lint and transpile
• The source still has no dependency and can be run on Node >= 0.8 but the dev environment will work with Node >= 4 (6 preferred).
• Upgrade of all dev dependencies.

Publishing

Open to suggestions - I'm planning on publishing a 1.0.0beta version of the package first, before making it official and stable. I'm not too worried but I could have missed something. 🤞

TODO

• Changelog
• Bump the version

Review

Tests have been ported to JS as well, but if you could make sure that the source files (especially the main src/index.js) doesn't introduce regression, that would be fantastic.
Any additional tests are very welcome as well.

Testing

• Clone the repo and checkout this branch. I personally linked the local branch and installed it in another repo to test imports were still working.

git clone https://github.com/florrain/locale.git
cd locale
git checkout repo-upgrade
npm install
npm link

cd ../express-application
npm link locale # install local version of the package

• Fire up an Express application
• Register the middleware
• Define a route to print the locale
• Send a request with the "Accept-Language" header and check it is working as expected.

Something like this:

import http from 'http';
import express from 'express';
import locale from 'locale';

const app = express();
app.server = http.createServer(app);

app.use(locale(['en', 'de'], 'en'));

app.get('/', function (req, res) {
  res.json({ headers: req.headers, locale: req.locale });
});

app.server.listen(process.env.PORT || config.port);

console.log(`Started on port ${app.server.address().port}`);

[zmagauina-fn]

@florrain Can I help get these changes merged in?