Merge: lib: add new lib `event_queue` a data-structure to manage queue of events

The objective is to be simple to use, powerful, efficient and flexible.

* simple to use:  no framework, only two public concrete classes, a lot of documentation
* powerful: instant, infinite and timed events, dynamic addition and removal of events, a lot of event information (time, duration, completion ration) , fluent-programming-capable
* efficient: internal use of heap and deadlines
* flexible: agnostic of time units, generic (use whatever you want in your events)

It initially targeted the management of the orchestration of graphical effects in a videogame, but become more general and useful.

Signed-off-by: Jean Privat <jean@pryen.org>

Pull-Request: #1939
Reviewed-by: Alexis Laferrière <alexis.laf@xymus.net>
Reviewed-by: Alexandre Terrasa <alexandre@moz-code.org>