migrate to Zensical

[boegel]

Material for MkDocs (MtM) is being sunsetted (see here).
Zensical looks like an interesting replacement, by the same authors of MtM, but it's currently not feature complete yet - there's no equivalent functionality yet for some plugins we are using:

• mkdocs-redirects (see Support mkdocs-redirects plugin functionality zensical/backlog#23);
• mkdocs-git-revision-date-localized-plugin (see Support mkdocs-git-revision-date-localized plugin functionality zensical/backlog#18);
• mkdocs-autorefs (see Support mkdocs-autorefs plugin functionality zensical/backlog#89);
• mkdocs-gen-files (see Support mkdocs-gen-files plugin functionality zensical/backlog#8);
• mkdocs-literate-nav (see Support mkdocs-literate-nav plugin functionality zensical/backlog#13);
• mkdocs-macros-plugin (see Support mkdocs-macros plugin functionality zensical/backlog#16);
• mkdocs-section-index (see Support mkdocs-section-index plugin functionality zensical/backlog#20);

Blogging support is also not available yet, see zensical/backlog#30.
That's important for the EasyBuild blog.