Introduce CI and releases

[cynthia]

It came to realization that 1) it is possible to break the build as our CI comes in too late, and 2) we have no change log or versioning the document. We should fix this.

#407

[LeaVerou]

From our discussion in yesterday's breakout: we can use GitHub releases here, to make it easier to generate a changelog as a starting point (GitHub's "generate release notes" feature automatically pulls in all merged PRs, then we can edit from there).

That doesn't solve the CI issue of course. @plinss is of the opinion we should just use our own server, I think it's easier to use something like Netlify or even GitHub Actions so we don't have to worry about maintenance and server upgrades.