Window event tracking

Each window allows you to track events occurring with it (for example, its movement). Each event can have its own callback function. To do this, use the addEventListener method, which is exactly the same as the components and has the following form:

void addEventListener(const string& action, 
                      function<void(window* sender, Event* e) callback>);

Windows can track the following events:

Action	Description
shown	Window has been shown
hidden	Window has been hidden
exposed	Window has been exposed and should be redrawn
moved	Window has been moved to data1, data2
resized	Window has been resized to data1xdata2
minimized	Window has been minimized
maximized	Window has been maximized
restored	Window has been restored to normal size and position
enter	Window has gained mouse focus
leave	Window has lost mouse focus
focus_gained	Window has gained keyboard focus
focus_lost	Window has lost keyboard focus
close	The window manager requests that the window be closed
take_focus	Window is being offered a focus
hit_test	Window had a hit test that wasn't SDL_HITTEST_NORMAL

data1 and data2 are the fields of the window structure of the Event union (for example, access to the data1 field looks like this: e->window.data1).