Website: Consolidate documentation pages for easier reading.

* Consolidate the "Client Integration" and "Server Integration" pages into
  the "Get Started" page, as they provide only basic information.
* Remove the "Basic" directory, as it is now empty.
* Rename the "Advanced" directory to "Features", as the contained pages don't
  actually describe advanced usage, only core features.
* Make minor wording tweaks.
Done, thanks