Some bugfixes and DNA reading / writing.

Session writing can be used to continue interrupted run.

    ./mona -S -o vector.png mona.png
    # (after 12 hours) ctrl+C , killall -9 mona, power outage, kernel panic, etc
    # then we continue
    ./mona -S -o vector.png mona.png vector.png.dna

But NUM_SHAPES and NUM_POINTS must match previous run :(