Documentation doesn't build with current gtk-doc

[nijel]

The GTK-Doc 1.26 has removed tmpl support and because of this the generated enca docs is mostly empty at it is mostly documented there.

Probably it is needed to move tmpl content to the header files, but my gtk-doc knowledge is close to zero.

[nijel]

Quoting from https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=841644#32:

My limited[1] knowledge on this matter makes me thing that templates
are completely out, so the headers/code would have to include
explicitly what it was in templates before.

There seems to be a direct mapping between the contents of the sgml
files ("SECTION Short_Description", "SECTION See_Also", "SECTION
Title", "SECTION Image", etc.) with @short_description, @see_also,
@image, @title etc. as described in:

https://developer.gnome.org/gtk-doc-manual/unstable/documenting_sections.html

Since in the sgml templates the sections are sometimes empty, I
suspect that most of the job would be to map the specific enums to
the
correct files in the code where they are relevant.

I am afraid that I am not familiar with the code, so I cannot be of
much help on that front.

[1] I've never used gtk-doc before, never even programmed with gtk
libs

[nijel]

I've created a workflow to build and publish the docs based on the script which used to run on my server - https://github.com/nijel/enca/blob/master/.github/workflows/docs.yml

The docs still needs fixes to make it build, this can just make testing a bit easier.