Add login / logout / get profile example

The 'quick start' code snippets provided in the documentation can be quite confusing, so I created a fully functional simple script for basic authentication (login), deauthentication (logout) and profile retrieval (GET /me). It helped me understand how the SDK works and I think it may help others too.

Usage and setup is explained in the script's comments, but it is as simple as cloning the repo on a public web server folder (whose domain must be allowed on the app settings) and setting the 4 parameters: app id, app secret, login url, logout url. Then you can test the SDK functionality just by hitting the script's URL on your browser.