Input.KeycodeKeyboard key code.
See https://github.com/torvalds/linux/blob/master/include/uapi/linux/input-event-codes.h
val of_int : int -> tval of_uint32 : Unsigned.UInt32.t -> tval to_uint32 : t -> Unsigned.UInt32.tval key_esc : tval key_enter : tval key_space : tval key_tab : tval key_home : tval key_end : tval key_left : tval key_right : tval key_up : tval key_down : tval key_pageup : tval key_pagedown : tval key_backspace : tval key_delete : tval btn_left : tval btn_right : tval btn_middle : t