Update the Getting Started section

Closes #49

See merge request !72

 - Fix the missing links to the API reference
 - Fix the missing links to various documentation sources
 - Use a slightly improved wording

Since it's available on freedesktop.org, instead of gnome.org.

Restore the list of points that was there in the old page.

Add back the setuid.html page

Closes #47

See merge request !70

The page is referenced by GTK's source code in a user-visible error
message, and we need to maintain the URL.

Fixes: #47

Update Javascript API reference link.

See merge request !68

Update links in macos.md after Gitlab migration

See merge request !65

Add gotk3 Go library to bindings doc

See merge request !66

In Controlling Event Handling normal is highlighted

See merge request !69

Minify HTML

See merge request !67

Fixes #39, only use scss

Closes #39

See merge request !64

Added Perl example

See merge request !63

Fix a typo in getting-started.md

See merge request !62

Adds how to run the Javascript Hello World App

See merge request !41

style: add bg color for hero

See merge request !61

Organized team section and some spacing

See merge request !60

Various fixes

Closes #31

See merge request !58

The subordinate clause does not contrast enough with the main clause to
justify a comma.

Split the stable and devel tags

Closes #25

See merge request !55

Remove mentions of DevHelp on Windows

Closes #30

See merge request !57