Express.js Sessions Store Abstraction Library

* Last tests against master on CircleCI: 

* Install with: npm install somesession

* Beware somesession would only pull all its depdencies if installed with its devDependencies.

Considering production deployments, you would have to pick from these devDependencies, those you would actually rely on.
Include them from whatever parent project or other piece of code you'ld be loading somesession from.

* Write backend-agnostic code:

``
// cassandra
const storeOptions = { driver: 'cassandra', database: 'sessions', username: 'casuser', password: 'caspass', host: '3.4.5.6', table: 'sessions' };
// mysql
const storeOptions = ({ driver: 'mysql', database: 'sessions', username: 'myuser', password: 'mypass', host: '2.3.4.5', table: 'sessions' };
// postgres
const storeOptions = ({ driver: 'postgres', database: 'sessions', username: 'pguser', password: 'pgpass', host: '1.2.3.4', table: 'sessions' };
// redis
const storeOptions = ({ driver: 'redis', database: 0, password: 'redisauthpass', host: '4.5.6.7' };
// defaults to sqlite
const storeOptions = ({ database: 'sessions.sqlite', path: './', table: 'sessions' };

const bodyParser = require('body-parser');
const express = require('express');
const http = require('http');
const session = require('express-session');
const store = require('somesession');

const app = express();
app.use(bodyParser.json());
app.use(bodyParser.urlencoded({ extended: true }));

const storage = store(storeOptions, session);
app.use(session({
cookie: { secure: process.env.NODE_ENV === 'production' },
store: storage, secret: 'secr3t',
resave: false, saveUninitialized: false,
cookie: { maxAge: 86400 }
});

const httpServer = http.createServer(app);

app.get('/', (req, res) => {
if (req.session !== undefined && req.session.userid !== undefined && req.session.userid !== false) {
res.send(req.session.userid);
} else { res.send('unauthenticated'); }
});

app.post('/login', (req, res) => {
let userId = req.body.userId || false;
if (userId !== false) { req.session.userid = userId; }
res.redirect('/');
});

app.post('/logout', (req, res) => {
if (req.session !== undefined && req.session.userid !== undefined && req.session.userid !== false) {
req.session.userid = false;
req.session.destroy();
delete req.session;
}
res.redirect('/');
});

port = port || 8080;
httpServer.listen(port, '127.0.0.1', (err, res) => {
if (err) { reject(err); }
console.log(mock server listening on 127.0.0.1:${port});
resolve(httpServer);
});
``