Reads the FAM file.

def _read_fam(self):
        """Reads the FAM file."""
        # Reading the FAM file and setting the values
        fam = pd.read_csv(self.fam_filename, delim_whitespace=True,
                          names=["fid", "iid", "father", "mother", "gender",
                                 "status"],
                          dtype=dict(fid=str, iid=str, father=str, mother=str))

        # Getting the byte and bit location of each samples
        fam["byte"] = [
            int(np.ceil((1 + 1) / 4.0)) - 1 for i in range(len(fam))
        ]
        fam["bit"] = [(i % 4) * 2 for i in range(len(fam))]

        # Saving the data in the object
        self._fam = fam
        self._nb_samples = self._fam.shape[0]