feat: add support to custom javascript

 - [ ] `data-gpz-action-up`
 - [ ] `data-gpz-action-down`

### html5 attribute
```html
<canvas class="gpz-btn" data-gpz-action-down="console.log(this)"></canvas>
```

### callback

```javascript
document.querySelectorAll('.gpz-btn').foreach(el => {
  el.addEventListener('gpz-action-down', ev => {
   console.log(ev)
 })
})
```