`gears.wallpaper` is a flat API (that doesn't even belong in gears) and
is neither well integrated with the other AwesomeWM concepts, nor well
documented or easy to understand for newcomers.
This module adds an object oriented, declarative, module with properties
for the most common wallpaper types. It also integrates with
`awful.placement` and the `wibox` module.
The design attempts to make the wallpaper a "wibox like" object like
the titlebars. It is non-interactive, but still allows the widgets. Note
that this is slow and should be avoided for dynamic content. It is why
the widgets are never updated unless manually reloaded. The objects also
attempt to be disposable rather than persistent. Thus they are immutable
by default to prevent accidental abuse.
Fix#3428#2596