Window resize events

resize_w, resize_h

When SDL_RESIZABLE is passed as a flag to SDL_SetVideoMode the user is 
allowed to resize the applications window. When the window is resized 
an SDL_VIDEORESIZE is reported, with the new window width and height 
values stored in the resize structure's resize_w and resize_h. When an 
SDL_VIDEORESIZE is received the window should be resized to the new 
dimensions using SDL_SetVideoMode.