typedef struct {
window_size_t x;
window_size_t y;
} window_s;
window_s cliwininfo();
this utility function gets the width and height of a terminal window (in terms
of characters), and returns it in a window_s struct.
window_size_t is just a name for an unsigned short because that's what
ioctl() internally returns the dimension sizes as.
window_s.x is the amount of columns.
window_s.y is the amount of rows.
this utility function can be used for all kinds of purposes but internally,
any kind of text centering utility such as clicenter_vert (see ezcli/clicenter)
uses cliwininfo().