Reported by:	Pau Amma

* Allow to build the documentation offline using Hugo
* Fix link problems
* Remove SVN entities
* Fix lang problems to help weblate
* Move all the AsciiDoctor translations to the shared folder to
  help weblate
* Allow the possibility to build each document. For example each
document can be edited in and watched the result in real time in
VS Code or Vim/NeoVim.

Breaking changes:

Eliminate the possibility of building books or articles.
They must be builded at the same time.
This functionality will be restored when version 0.89.0 is in the
repositories in a couple of weeks.

Reviewed by:            dbaio@
Differential Revision:  https://reviews.freebsd.org/D31926

This reverts commit 3462d12db6ebf303064db168a2333374344f369a.

Too soon, it broke asciidoctor-pdf which doesn't know Hugo's shortcode.
It will take more time and care.

This is a prerequisite for the translation workflow through .po files
and Weblate.

The asciidoctor include with the shortcode variable will help because
won't be needed to change the includes manually after converting the
translation (.po file) back to .adoc.

It will help other areas like, language attributes, which today is fixed
in every document.

The use of shortcode was suggested by jmooring@ from Hugo's project on
Github.

Reviewed by:	carlavilla
Differential Revision: https://reviews.freebsd.org/D30823

Approved by:	carlavilla

I'm very pleased to announce the release of
our new website and documentation using
the new toolchain with Hugo and AsciiDoctor.

To get more information about the new toolchain
please read the FreeBSD Documentation Project Primer[1],
Hugo docs[2] and AsciiDoctor docs[3].

Acknowledgment:
Benedict Reuschling <bcr@>
Glen Barber <gjb@>
Hiroki Sato <hrs@>
Li-Wen Hsu <lwhsu@>
Sean Chittenden <seanc@>
The FreeBSD Foundation

[1] https://docs.FreeBSD.org/en/books/fdp-primer/
[2] https://gohugo.io/documentation/
[3] https://docs.asciidoctor.org/home/

Approved by:    doceng, core