Changed license from LGPL to the zlib license

The license of these bindings now match the license of Box2D itself.
This change makes it possible to embed this code in commercial
applications without restrictions. This was mainly done because shipping
dynamic libraries can be problematic on mobile platforms.

All contributors have agreed to this licensing change.
Updated the COPYING file with the new license
Updated to Box2D v2.2.1
Merge branch 'master' into qt5
Changes for Qt 5 release