input: Write a python function to check if a class is a subclass of another class.
  assert is_subclass(Derived, Base)==True
  assert is_subclass(SingleInheritance, Base)==True
  assert is_subclass(MultipleInheritance, Derived)==True
  assert is_subclass(Base, Derived)==False
output: def is_subclass(cls, parent_cls):
      return issubclass(cls, parent_cls)