Reduce memory footprint

Original library dropped the buggy RGB stuff and reduced samples to just:
```const cubes: number = Math.pow(sides, 3);``` packed to `0b00YYhhll`

https://github.com/darosh/colorgram-js/blob/4302c3d1e3116ecc70c2557533674322b5d95b82/src/colorgram.ts#L45