Create a replace document and add it to the list of ops.

def add_replace(self, selector, replacement, upsert=False,
                    collation=None):
        """Create a replace document and add it to the list of ops.
        """
        validate_ok_for_replace(replacement)
        cmd = SON([('q', selector), ('u', replacement),
                   ('multi', False), ('upsert', upsert)])
        collation = validate_collation_or_none(collation)
        if collation is not None:
            self.uses_collation = True
            cmd['collation'] = collation
        self.ops.append((_UPDATE, cmd))