support outer join #98
Description
claims just supports cross join and equal join now, correspond to nest loop join and hash join, and doesn't support outer join now. outer join contains left outer join, right outer join and full outer join. if join condition is false, then all cell value of one tuple is null in some table.
you need add logical operator and physical operator of outer join in logical_operator folder and physical_operator, and add them into makefile and common/serialize/RegisterDerivedClass, also comments and test case should be complete.
you can refer to the implementation of cross join and equal join.