Convert headers into valid namedtuple fields.

def _init_nt_hdr(self, line):
        """Convert headers into valid namedtuple fields."""
        line = line.replace('.', '_')
        line = line.replace(' ', '_')
        line = line.replace('#', 'N')
        line = line.replace('-', '_')
        line = line.replace('"', '')
        #line = re.sub(r"_$", r"", line)
        hdrs = re.split(self.sep, line)
        if '' in hdrs:
            hdrs = NCBIgeneFileReader.replace_nulls(hdrs)
        # Init indexes which will be converted to int or float
        self.idxs_int = [idx for idx, hdr in enumerate(hdrs) if hdr in self.int_hdrs]
        self.idxs_float = [idx for idx, hdr in enumerate(hdrs) if hdr in self.float_hdrs]
        assert hdrs[6] == 'Aliases'
        return namedtuple('ntncbi', ' '.join(hdrs))