This function registers the files that will be saved in GridFS.
        kwargs is a dictionary mapping the key associated to the file (usually the extension)
        to the absolute path. By default, files are assumed to be in binary form, for formatted files
        one should pass a tuple ("filepath", "t").

        Example::

            results.register_gridfs(GSR="path/to/GSR.nc", text_file=("/path/to/txt_file", "t"))

        The GSR file is a binary file, whereas text_file is a text file.

def register_gridfs_files(self, **kwargs):
        """
        This function registers the files that will be saved in GridFS.
        kwargs is a dictionary mapping the key associated to the file (usually the extension)
        to the absolute path. By default, files are assumed to be in binary form, for formatted files
        one should pass a tuple ("filepath", "t").

        Example::

            results.register_gridfs(GSR="path/to/GSR.nc", text_file=("/path/to/txt_file", "t"))

        The GSR file is a binary file, whereas text_file is a text file.
        """
        d = {}
        for k, v in kwargs.items():
            mode = "b"
            if isinstance(v, (list, tuple)): v, mode = v
            d[k] = GridFsFile(path=v, mode=mode)

        self["files"].update(d)
        return self