Build offline documentation using Hugo and other improvements

• 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