tutorials: Add note on ensuring custom types in templates

See merge request !120

tutorials Add section on GApplication's command line handling

See merge request !119

Otherwise the GtkBuilder parser won't know what type to instantiate.

Port the GtkApplication/CommandLine HowDoI, so we can redirect
the wiki page to the developer docs website.

Fix Vala examples in Getting Started

See merge request !114

Minor changes to save_file function. Fixes a couple runtime assertion
failures and syntax errors.

Use a closure for handling the async finish function in all examples.

Add a missing trailing slash.

See: Infrastructure/Infrastructure#939

Update the themed icons tutorial

See merge request !104

beginners: Fix typo in menu_button tutorial

See merge request !110

Fix link to HIG

Closes #46

See merge request !111

- needs a trailing / now

Fixes #46

Improve component tutorial for radio buttons

See merge request !109

The GVariant specification uses secnum to provide stable section
numbering, but Sphinx doesn't really like that pragma; the numbering
starts from the title, when in reality it should start from the content.

The fix-secnum extension takes care of that.

Add the GVariant specification

See merge request !108

Philip made the images, but the spec was originally written by Allison
and just ported to reStructuredText.

GLib added it in tree, and we can publish it on developer.gnome.org as
part of a larger effort to move some of our interoperability specs out
of random locations or, worse, the wiki.

Contrary to Netlify, GitLab Pages do not support redirecting to external
websites.

This reverts commit 2c74c97f.

valgrind: Remove unneeded option

See merge request !107

The leak resolution option is by default set to "high"

1. Recommend resources for assets shipped as named icons.
2. Ensure that people call gtk-update-icon-cache when installing icons
   as files

Otherwise reStructuredText will complain.

Add Tools section

See merge request !102

The dep5 syntax for Copyright allows multiple lines, but dep5 disallows
duplicates.

Taken from Christian's blog:

  https://blogs.gnome.org/chergert/2020/03/14/how-to-use-sysprof-to/

Needs a refresh of the images.

Newcomers and experienced developers alike should know the kind of tools
useful when developing, debugging, and profiling GNOME apps and
components.

Port the missing section from the optimization guide on the old
developer docs website.

Tutorials: Port drag and drop to Vala

See merge request !94

Update stack.rst to properly display some code blocks

See merge request !100