Automatic deployment of the Effekt compiler to the website

[b-studios]

Right now, the only two people how know how to update the Effekt compiler on our website are @jiribenes and I. It is a manual process of:

1. building the JavaScript hosted version (e.g., sbt fullOptJS)
2. copying the generated file to https://github.com/effekt-lang/effekt-website/blob/master/src/effekt.js
3. running webpack
4. adding, comitting, and pushing the dist files generated by webpack. (for example: https://github.com/effekt-lang/effekt-website/commit/547ca609fa12076be4ddee439c14eeb3aedb323f)

Maybe we want to automate this process? I don't know exactly which form of automation we want. Two trigger options come to mind:

1. On every commit to effekt/master
2. On every version / tag on effekt/master

One thing to keep in mind is that I haven't created a "release" in a while. If we keep that release schedule (which is random and almost never :) ), then the website won't be updated. It is nice to have nightlys on the website, however it could also break the website and we do not have sufficient tests to rule that out.

WDYT?

[jiribenes]

I thought about the possible triggers -- why not both nightly and a "latest tagged version"? We could have one of those by default and let the user select the other if they want to do so, similarly to how Rust Playground does it:

[b-studios]

Implemented by @dvdvgt