Rename of elapsed_time to delta_time
Rename of onExit to onQuit
Rename of method Load to onInit
Rename of method onClose to onExit
Update comments (spacing & doxygen)
(Re)-Add keyboard bindings for placing cards on board with keys 1..9
Add CardDebug object to private scope from local scope
Prettify spacing of method arguments
Re-arrange order of header file deps