add ProgressBar example application
remove deprecated variables for Doxygen
Updated AUTHORS file.
Updated renderer to work with new SFML texture binding.
Optimized primitive construction and label resizing.
Implemented SpinButton, fixed a few typos.
Fixed sf::Event::MouseEntered and sf::Event::MouseLeft not being handled properly, moved bit field manipulations into their own methods.
Implemented a widget registry that tracks all root level widgets, fixed widgets not automatically refreshing when their ID or class is changed, fixed widgets not automatically refreshing when a property is changed after their drawables are constructed (for all future Engine writers: call SetAutoRefresh( true ) AFTER you are done setting the initial properties to enable this functionality with your Engine as well), changed RemoveAll functionality in Container to be more consistent with Remove functionality, added ability to search for Widgets by class or ID to support "create and forget" coding style.
Added changelog. Fixed uninitialized variable (#586).