Fixed references to CallbackHandlerInterface in php-io

Signed-Off-by : Grégory PLANCHAT <g.planchat@gmail.com>
Updated composer.json to PSR-4

Signed-Off-by : Grégory PLANCHAT <g.planchat@gmail.com>
Merge remote-tracking branch 'origin/master'

Conflicts:
	src/EventEmitterTrait.php