Draft: Prep v0.4.0 website

[dgkf]

Aiming to get a few new website features in place for this release:

• Move the web repl to a /live url
• Publish crate documentation (and ideally have live repls in examples)
• Have a news page that highlights what is new in the latest release

Long term, if it grows any larger and would benefit from a site generator that brings a considerable dependency overhead, then I think the website should probably be split off into a separate repo.

For this release, I intend to still have a rather simple diy site.

[dgkf]

@sebffischer - I put together a small release notes webpage. Feel free to take a look. Please let me know if there's anything you'd like to change before it gets publicized.
https://dgkf.github.io/R/release/v0.4.0/

Also, prompted by your anecdote about the discoverability of available functions, I added docs for all the primitives we have. And you can execute examples in the browser! Not necessarily ideal, but a easy enough middle ground until we have proper help files.
https://dgkf.github.io/R/docs/r/callable/primitive/struct.PrimitiveRunif.html

[sebffischer]

@dgkf Awesome, this is just what we needed! I also love that the examples can be executed, wasm is just such a nice technology!

• In R, modifying this interior data comes at a steep cost since each view is copied for modification and then a new copy
  of the original data is created prior to insertion of newly modified contents.

  I think the copy of the original data is only created if there is more than one "lazy-copy" of that list, which R tracks in a a single bit that indicates whether there is exactly one "lazy copy" of the data (when it mutates in place) or more than one (than it copies). (However, because there is a single bit to track this, R is unable to decrement the Ref counter when there were three such copies but one goes out of scope).

• The "Play" bottom on the top-left still points to your personal website and the "Docs" button 404s.
  Both are because the links are relative to "https://dgkf.github.io/" instead of "https://dgkf.github.io/R/"