Upgrading to ES2021

[egekorkan]

As agreed last week, we will upgrade to Node.js ES2021 and if it doesn't work, we can go for older versions. We will bump minor version, i.e. going to 0.9.0.

We will merge #1266 and #1258 before doing that.

[relu91]

Tried to upgrade to ES2021 and as @danielpeintner predicted something broke. It seems that browserify can't handle modern js syntax out of the box. Instead of keeping personalizing browserify I would prefer to upgrade to more modern solutions and therefore this issue is blocked by: #387

[egekorkan]

We can try something like https://parceljs.org that allows customization (we can use readable stream 4) and is new and fast.