mraa: new package

mraa provides a unified interface for IO on Galileo, Edison,
Raspberry Pi and others.

Signed-off-by: Pieterjan Camerlynck <pieterjan.camerlynck@gmail.com>
Tested-by: Samuel Martin <s.martin49@gmail.com>
Acked-by: Samuel Martin <s.martin49@gmail.com>
Reviewed-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>