Higher level content negotiation based on negotiator.

In addition to negotiator, it allows: - Allows types as an array or arguments list, ie `(['text/html', 'application/json'])` as well as `('text/html', 'application/json')`. - Allows type shorthands such as `json`. - Returns `false` when no types match - Treats non-existent headers as `*`

Node.js is an event-based server-side JavaScript engine.