Get module speed benchmarks to appear in a PR comment

[jywarren]

We could use https://danger.systems/js/ to collect the benchmark times and add them to each PR so you can easily read them. We could use the HTML <details> element to hide them unless you want to see them:

<details>
    <summary>📊 Benchmarks (click to expand)</summary>
    <p>Benchmarks are run on each module</p>
    <ul>
      <li><b>Average</b>: 341ms</li>
      <li><b>Blur</b>: 441ms</li>
      <li><b>Blend</b>: 141ms</li>
      <!-- ... -->
    </ul>
</details>

This would be pretty neat! We could also actually eventually output test image outputs that could be visually reviewed.

[vibhorgupta-gh]

Related to #780
WIP.