/* 
 * Return the number of this Joystick::Event object.
 *
 * The value of Joystick::Event#number is the axis or button of the
 * event.
 *
 * Aliases:
 *   Joystick::Event#num
 *
 * Example:
 *   puts "You're using joypad #{(ev.num / 2) + 1}." \
 *     if ev.type == Joystick::Event::AXIS
 *
 */
static VALUE j_ev_number(VALUE self) {