Update dependencies and publish the rollup-plugin-postcss fork?

[mihkeleidast]

Hi @LukeChannings! First of all, thanks for this example repository! I've been trying to figure out how to setup a tree-shakeable component library, so this definitely helped out.

I wanted to raise two issues/questions:

1. I had trouble getting this repository to work at first. When trying to build the component-library, some dependencies were missing and the build failed. I kind of fixed that by updating and re-installing a lot of the dependencies. Not sure what was wrong here, maybe our Node/npm versions are incompatible or things have just broken with the times. Either way, I pushed the updates to my fork - let me know if you'd accept a PR here, I can clean that up.
2. As far as I can understand, your fork of rollup-plugin-postcss is still necessary to make this work properly. Is your version published to npm somewhere, or would you be willing to do that? I could fork and publish it myself as well, but maybe it already exists and I just can't find it. I feel like installing a fork directly from GH is not very suitable for real projects :) In addition, there doesn't seem to be a PR trying to contribute these changes back to the original repo - might be worth trying?

P.S. I also created a similar example using vanilla-extract, if interested. There doesn't seem to be too many good examples of tree-shakeable component libraries out there :)

Thanks again!