feat: playground/codepen

[hyrious]

Let's copy some ideas from https://sfc.vuejs.org (source: https://github.com/vuejs/repl).

[whatnickcodes]

This project is super cool - thanks for sharing. Would be awesome to see some sort of preview/render down the road!

[hyrious]

One good news is that evanw simulates a FS in the browser in https://esbuild.github.io/try/ via modifying the esbuild-wasm wrapper created by Go lang. Maybe I can learn this technique to make the codepen happen.