Add/register extensions.

        Args:
            exts (dict):
            force (bool): If ``force`` is set to ``True``, simply overwrite existing extensions, otherwise do nothing.
                If the ``logger`` is set, log a warning about the duplicate extension if ``force == False``.

def register_extensions(self, exts, force=False):
        """
        Add/register extensions.

        Args:
            exts (dict):
            force (bool): If ``force`` is set to ``True``, simply overwrite existing extensions, otherwise do nothing.
                If the ``logger`` is set, log a warning about the duplicate extension if ``force == False``.
        """
        for ext_in, ext_out in exts.items():
            self.register_extension(ext_in, ext_out, force)