CALHEIGHT and CALWIDTH defined
goto_day() prototype updated to take into account date_t type
calendar_store_current_date() created
calendar_goto_day() moved to calendar_change_day()
calendar_get_slctd_day() and calendar_get_slctd_day_sec() added
calendar_init_slctd_day() created
calendar_move_up(), calendar_move_down(), calendar_move_left() and
calendar_move_right() created
wday_t and date_t type defined
calendar_set_first_day_of_week(), calendar_change_first_day_of_week() and
calendar_week_begins_on_monday() created
