VTERM_KEY_FUNCTION_0
VTERM_KEY_FUNCTION_MAX = VTERM_KEY_FUNCTION_0 + 255,
#define VTERM_KEY_FUNCTION(n) (VTERM_KEY_FUNCTION_0+(n))
if(key < VTERM_KEY_FUNCTION_0) {
else if(key >= VTERM_KEY_FUNCTION_0 && key <= VTERM_KEY_FUNCTION_MAX) {
if((key - VTERM_KEY_FUNCTION_0) >= sizeof(keycodes_fn)/sizeof(keycodes_fn[0]))
k = keycodes_fn[key - VTERM_KEY_FUNCTION_0];