Example of running benchmarks in a browser

[ebrelsford]

I'm not sure if we want to include this (or this approach) but this was my initial take on running benchmarks in the browser. This PR:

• Adds a new benchmarks file geared toward the browser (fetch rather than fs)
• Adds a rollup config to build the bundle needed
• Loads benchmarks.js globally instead of bundling it (see this issue, it doesn't get bundled correctly)

[ebrelsford]

@springmeyer here is this PR in case it's useful.

[springmeyer]

Thanks! I'll take it for a spin soon and confirm it works for me.