Support #rgba hex strings

```
$ node example/parse.js '#f98'
{ rgb: [ 255, 153, 136 ],
  hsl: [ 9, 100, 77 ],
  hsv: [ 9, 47, 100 ],
  cmyk: [ 0, 40, 47, 0 ],
  keyword: undefined,
  hex: '#ff9988',
  rgba: [ 255, 153, 136, 1 ],
  hsla: [ 9, 100, 77, 1 ],
  hsva: [ 9, 47, 100, 1 ],
  cmyka: [ 0, 40, 47, 0, 1 ] }
```

```
$ node example/parse.js '#333'
{ rgb: [ 51, 51, 51 ],
  hsl: [ 0, 0, 20 ],
  hsv: [ 0, 0, 20 ],
  cmyk: [ 0, 0, 0, 80 ],
  keyword: undefined,
  hex: '#333333',
  rgba: [ 51, 51, 51, 1 ],
  hsla: [ 0, 0, 20, 1 ],
  hsva: [ 0, 0, 20, 1 ],
  cmyka: [ 0, 0, 0, 80, 1 ] }
```