Doxyfile: Add other directories
Fix GCC build issues with non-POD in union
Crowd: Fix intermittent crash. See issue #67.
Documentation: Add main page
Doxyfile: Do not extract private class fields
Doxyfile: Do not sort declarations
Type: Add POD typedefs
Engine: Tweak class description
Engine: Document method return values
Engine: Pure virtual destructor
Bakge: Split platform headers into two
Engine: Fix pure virtual destructor declaration
Engine: Add *structor documentation
Engine: Update documentation
EventHandler: *structor documentation
Window: *structor documentation
Window: Default constructor now protected
Input: File description tweak
Window: File description added
Shape: Add documentation