Reassign key layout (e.g. from A-B to A-Z)

In my opinion the usage of `A` , `B` , `SELECT `and `START` (as labels) is very appropriate considering structure of the classical controllers. However when using a regular keyboard as input interface, the distance between the keys 'A' and 'B' makes the experience very hard. Is almost impossible to achieve any natural mechanics.

What do you think about providing a way to re-map the default keys to a custom layout ?

Something like this l:
`inputMap( keyboardKeyID , controllerButtonID ) `
Generate a binding between the provided key, and one of the four available buttons.

```javascript
// Map any press on the key 83 ('S') to the key B
inputMap( 83 , 'B' );
// Map any press on the key 68 ('D') to the key SELECT
inputMap( 68 , 'SELECT' );
```

Inizia individuando la gestione dell’input da tastiera e le associazioni predefinite di A, B, SELECT e START descritte nell’issue. Determina come dovrebbe essere esposta e resa persistente un’associazione personalizzata tasto-pulsante, quindi verifica che i tasti rimappati attivino i pulsanti del controller previsti senza compromettere le associazioni predefinite.

Scritto dal modello di indicizzazione a partire dal testo della issue.