[DOC] Documentation website

[ankurankan]

Idea:

• A single website for the Rust core as well as bindings.
  - Will reduce maintenance work.
  - Less content to write.
• For code examples, show the user the option to choose between Rust, R, Python, JS.
• mdbook seems to be the sphinx equivalent in Rust. Combined with mdbook-langtabs plugin, it seems to be possible to generate such a doc website.

Implementation:

• Create a new crate for documentation. The target should be a separate repo that we can render using GitHub Pages.
• Add doc building options to the Makefile.