Random building sites left

This is an intermediary commit which may be (very likely) vanish in the
course of a git rebase of this whole bunch of shitty non-concrete commits.

I want to work on it tomorrow at school so this commit is really necessary
and includes really a whole lot of building sites which I try to
re-understand after this long break.

Tomorrow, I want to get the X/Y-based optimisation done to implement tile
optimisation so that at least the laytest example works again... Hopefully.
I didn't analyse the entire program but it seems that tgfb_fb_draw_tile()
currently blocks all output from happening.