We should at least check that Devhelp builds correctly.

This reverts commit 18369a69.

amtk is now archived.

- Update/Add App icon as svg
- Update/Add trail link

The existing maintainers have either stepped back a long time ago, or
have stopped contributing everywhere else.

I am happy to pick up Devhelp in the interim.

The revert in 1d5c8da1 generated two
compiler warnings, so let's get rid of those.

The stable branch for Devhelp 40 is: gnome-40.

The WebKitSettings:enable-plugins property is deprecated in WebKitGTK
2.32, and setting it does not do anything.

Clean up the top level directory of the repository.

It's just old cruft, at this point; it is still available in the commit
history, so we don't need to have it lying around.

The authors are in the commit log.

GitLab recognises the presence of a "CONTRIBUTING.md" and links it from
the project's main page.

Use the basic template from Nadia Eghbal, adapted for the GTK project.

See: https://github.com/nayafia/contributing-template

Use different sections for different build options.

Use a single, parametrised script, instead of three separate, hard coded
ones.

We only want the warnings.

Ensure that the desktop file is valid at build time, including eventual
translations.

The application menu has been dropped from GNOME for a while, now;
there's no need to have a fallback in place.

Drop the "Quit" element: there is a "close" button right next to the
menu button.

Drop the single element section for the "Preferences" element, and
instead group it with the rest of the application-level actions.

Fixes: #27

During the GNOME development cycle we want to visually distinguish the
development builds of Devhelp from the stable, system one. Additionally,
we want to be able to run the two builds at the same time.

And add a manifest for the stable profile.

Newer Meson versions need an explicit dependency for the test() targets.

We should look for DevHelp books under XDG_DATA_DIRS/doc,
XDG_DATA_HOME/doc, and the Flatpak host /usr/share/doc directories. Not
every API reference is built with gtk-doc, or installed under the
DevHelp directory.

Fixes: #29

We should allow modern API references to detect when running under
DevHelp, and update their style in ways that improve integration.

See: #28

We add a custom class, called "devhelp-hidden", that can be used by
tools generating the documentation to hide UI elements that should not
be visible when browsing the HTML in DevHelp.

(cherry picked from commit 0226f1f4a9d9fb04237bff0bcdec746499a2b7e2)

We don't need it any more, and it's been dropped from GNOME.

We have to use `validate-relax` because the `validate` command is too
strict by default, and will choke on our captions and screenshot files.

The build sandbox does not have a network connection, so the validation
cannot reach the screenshots.

Move the description up top, and fix the link to the contribution
guidelines.

We want to be able to validate the appdata file even when building the
Flatpak bundle.

Fixes: #47

Document that we switched to `main`, and add instructions on how to
switch extant local checkouts.

The gi-docgen tool uses the introspection data, which means our API
reference will match the API available to our consumers across multiple
languages. Additionally, gi-docgen is faster than gtk-doc, and generates
a better HTML output that can be searched remotely outside of Devhelp.

We use gi-docgen for our API reference, now.

And publish our API reference on our Pages section.

The g_pattern_match_string() function has been deprecated in GLib 2.70
for the more appropriately namespaced g_pattern_spec_match_string().