Add support for table of contents
Currently gi-docgen doesn't generate a table of contents (TOC), it generates several indices instead (each index list its symbols alphabetically).
With gtk-doc, it is possible to create a TOC.
A TOC is useful to group related things together, in a same chapter. For example to regroup all the classes that are part of the same subsystem.
My personal opinion is that listing things alphabetically only works well for very small projects (with less than 10 classes, say).