$on with an array of events

Would be neat if `$on` supported an array of events:

```js
bus.$on(['CLICK_BODY', 'KEYUP_ESCAPE'], () => {
  this.active = false
})
```

Without it we need duplication

```js
bus.$on('CLICK_BODY', () => {
  this.active = false
})
bus.$on('KEYUP_ESCAPE', () => {
  this.active = false
})

// or

bus.$on('CLICK_BODY', deactivate)
bus.$on('KEYUP_ESCAPE', deactivate)
```