The `hide_from_sitemap` metadata variable was a custom thing we implemented
to add a "noindex" meta-header to pages and to exclude a page from the
search auto-complete.
However, pages with that option set would still be included in sitemap.xml,
resulting in search engines to visit those pages (only to discover they
should not index them).
This patch replaces the custom `hide_from_sitemap` value for `sitemap: false`,
which is a metadata variable that's defined by the "jekyll-sitemap" plugin
we use to generate the sitemap.xml;
https://github.com/jekyll/jekyll-sitemap/blob/v1.4.0/README.md#exclusions
Setting this variable will now:
- add a "noindex" metadata header to the page
- exclude the page from the sitemap.xml.
- exclude the page from /js/metadata.json (used for search autocomplete)
Also fixed an issue in the metadata.json where the `notoc` metadata was
used to exclude pages, however that variable is meant to disable the
in-page TOC (right-hand side navigation with anchor links).
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
