Method for writting a formatted <th> cell.

        If col_space is set on the formatter then that is used for
        the value of min-width.

        Parameters
        ----------
        s : object
            The data to be written inside the cell.
        header : boolean, default False
            Set to True if the <th> is for use inside <thead>.  This will
            cause min-width to be set if there is one.
        indent : int, default 0
            The indentation level of the cell.
        tags : string, default None
            Tags to include in the cell.

        Returns
        -------
        A written <th> cell.

def write_th(self, s, header=False, indent=0, tags=None):
        """
        Method for writting a formatted <th> cell.

        If col_space is set on the formatter then that is used for
        the value of min-width.

        Parameters
        ----------
        s : object
            The data to be written inside the cell.
        header : boolean, default False
            Set to True if the <th> is for use inside <thead>.  This will
            cause min-width to be set if there is one.
        indent : int, default 0
            The indentation level of the cell.
        tags : string, default None
            Tags to include in the cell.

        Returns
        -------
        A written <th> cell.
        """
        if header and self.fmt.col_space is not None:
            tags = (tags or "")
            tags += ('style="min-width: {colspace};"'
                     .format(colspace=self.fmt.col_space))

        return self._write_cell(s, kind='th', indent=indent, tags=tags)