Embedding assets into Go executable

Yes, this is super neat, because we can now commit embedded asset files directly, and they will get embedded at go build time instead of committing a large go module that contains embedded assets. In Simple IoT, we have refrained from committing the frontend assets (we’re still using Genesis), as it results in a 3.5MB Go module that bloats the repo, skews code metrics, etc. However, the JS module (compiled Elm) is only 161KB, so that seems a lot more reasonable. And we may be able to compress that more – if we xz the elm.js, it goes down to 43KB, and it would probably cost very little time to uncompress that in the HTTP api handler. Compiled Elm sizes are amazing.