Read the tumor and normal fastas into a joint dict.

    :param dict input_files: A dict containing filename: filepath for T_ and N_ transgened files.
    :return: The read fastas in a dictionary of tuples
    :rtype: dict

def read_fastas(input_files):
    """
    Read the tumor and normal fastas into a joint dict.

    :param dict input_files: A dict containing filename: filepath for T_ and N_ transgened files.
    :return: The read fastas in a dictionary of tuples
    :rtype: dict
    """
    tumor_file = [y for x, y in input_files.items() if x.startswith('T')][0]
    normal_file = [y for x, y in input_files.items() if x.startswith('N')][0]
    output_files = defaultdict(list)
    output_files = _read_fasta(tumor_file, output_files)
    num_entries = len(output_files)
    output_files = _read_fasta(normal_file, output_files)
    assert len(output_files) == num_entries
    return output_files