instantiate an observation obsemble from a jco-type file

        Parameters
        ----------
        pst : pyemu.Pst
            a Pst instance
        filename : str
            the binary file name

        Returns
        -------
        oe : ObservationEnsemble

def from_binary(cls,pst,filename):
        """instantiate an observation obsemble from a jco-type file

        Parameters
        ----------
        pst : pyemu.Pst
            a Pst instance
        filename : str
            the binary file name

        Returns
        -------
        oe : ObservationEnsemble

        """
        m = Matrix.from_binary(filename)
        return ObservationEnsemble(data=m.x,pst=pst, index=m.row_names)