Since it is used only one, use require() directly. This allows
to require it from `beautiful` without a circular dependency.
In turn, this allows to set colors using the rules rather than
adding an endless amount of theme variables.
This commit introduce the new "ruled" module. This new top level
module will eventually host all "rules" related modules.
As for the content of the commit, it adds rules for notification. They
are mostly identical to the client rules and can be used to customize
or filter the notifications. It replaces the old "preset" API. The
preset API inner working was mostly a duplication of the early
`awful.rules` API, but was never as flexible. Thus the idea behind this
work is to converge all "core" classes to use a similar declarative API.
Emmanuel Lepage Vallee