Scroll Sequence complete!

VBI scrolls trough a complete sequence of 6 screens, stoops, resets
scroll sequence, draws new play field and increases score. Source code
is still messy and comments are mixed german / english :)

Next goal: Write good playfield generator…..
Bird <=> background collision and colors added.

Now our bird dies, if it touches one of the obstacles.

Background is much nicer now :-)