Creates genome size dict from string containing data.

def create_genome_size_dict(genome):
    # type: (str) -> Dict[str,int]
    """Creates genome size dict from string containing data."""

    size_file = get_genome_size_file(genome)
    size_lines = open(size_file).readlines()

    size_dict = {}
    for line in size_lines:
        genome, length = line.split()
        size_dict[genome] = int(length)

    return size_dict