Fixed documentation
Merge pull request #44 from mateuszgachowski/master

Fixed documentation
Introduced new Engine class.

Core functionality has been moved to a namespaced Engine class. The
existing Flight class is now just a static pass-through to the Engine class.
Also fixed autoloading and initialization issues.
Merge remote-tracking branch 'origin/master'
Cleaned up initialization process.
Added example for new Engine class.
Fixed issue with 304 caching. Fixed PHP 5.3 compatibility.