Remove ostream parameter from print_title
Shorten names of private members of car_t
Add car_t::_date
Add getters to car_t

Add car_t::inventory_number()
Add car_t::date()
car_t::plate_num -> car_t::plate_number
Add iso646 to lot.h
Add inv_num_t
Fix lot_t data
Unfriend date_t::operator <<

make month() day() and year() const
Add < comparison operator for date_t
Move date ctor and getter definitions to date.cpp