Rewrite to Astro, to make the website static

[DLakomy]

Fixes #117

Hello.

I've learned Astro yesterday and thought I might try rewriting your webpage to a static one. I've got nothing against JavaScript on your page, but saw an issue on GitHub.

What I optimized for:

1. Similarity to React, so the current maintainers have no trouble switching. This is why I chose Astro.
2. Limited refactors, so it doesn't take long to implement (it's difficult to merge updates from master during a full rewrite).
3. 100% similarity, pixel for pixel, to make it easier to review. I've spent hours tweaking it and trying not to leave accidental changes (especially in the content, it's surprisingly easy to loose a paragraph...), but to be honest I'm not 100% sure I've got everything. The icons are slightly different on the documentation subpage. I guess it's a matter of fontawesome's version.
4. Zero JavaScript at runtime (after running npm run build you can run find ./dist -name '*.js' and see no results).

Some notes:

1. There is a TODO comment in src/components/InlineEditor.astro. It's not blocking this merge, just a suggestion for the future. I guess this would help make Flix more popular (which I hope will happen!).
2. I've replaced the carousel (Visual Studio Code Support section on the home subpage) with a simple grid. I can try to make a pure CSS carousel, but maybe it should be removed and just point to the VSCode webpage. What do you think?

How to test:

1. npm run build.
2. Serve dist subdir. For example cd dist && python -m http.server 8000 and open http://localhost:8000/ in your browser. Actually, now you can even read that with curl :D
3. There is a question in FAQ: "This site requires JavaScript" and similar. Shall I redact them, as no longer standing?

If you're interested in merging, I'm waiting for your feedback and can check again before merging, to make sure no text is lost.