- Update to version 2021.7:
+ Add a "check" sub-command
+ Allow defining multiple content directories
+ Detect gtk-doc code blocks for JavaScript
+ Multiple changes to the basic template
+ Add in-page content navigation
+ Filter hidden data from indices
+ Allow defining hidden symbols matching a regular expression
+ Handle (attribute element-type) annotation for GListModel
+ Fix class method linking
+ Fix links to callback type arguments
+ Fix argument listing in class methods
+ Don't grab the 's' key when the sidebar is hidden
+ Index the extra content files for search
+ Fix gtk-doc sigil handling in code blocks
+ Re-instate gtk-doc `()` function detection
- Switch to building only default flavour of python3.