Move to PSR-4.

Signed-off-by: crynobone <crynobone@gmail.com>
Release v2.1.2

Signed-off-by: crynobone <crynobone@gmail.com>
Merge branch '2.1'

Signed-off-by: crynobone <crynobone@gmail.com>

Conflicts:
	src/Extension/Environment.php
	src/Orchestra/Extension/Environment.php
	src/Orchestra/Extension/Factory.php