Add error message for given field path.

        Example: ::

            builder = ValidationErrorBuilder()
            builder.add_error('foo.bar.baz', 'Some error')
            print builder.errors
            # => {'foo': {'bar': {'baz': 'Some error'}}}

        :param str path: '.'-separated list of field names
        :param str error: Error message

def add_error(self, path, error):
        """Add error message for given field path.

        Example: ::

            builder = ValidationErrorBuilder()
            builder.add_error('foo.bar.baz', 'Some error')
            print builder.errors
            # => {'foo': {'bar': {'baz': 'Some error'}}}

        :param str path: '.'-separated list of field names
        :param str error: Error message
        """
        self.errors = merge_errors(self.errors, self._make_error(path, error))