Part 10 - game UI and helper functions (random, add-score, level-init…

…, ...)

Now most of the elements (to assemble simple "game" out of this) are in
place, the only major item missing is scoring the "jump over snowball".

In this part 10 we did add UI elements like score/bonus/lives, they are
displayed in classic ULA layer, on "white" paper which is in palette set
to be transparent, and layers priorities were modified to "USL", so
these UI texts are above anything else (including sprites).

We added also simple random generator from Baze, and added some debug
features like random score increments to test new routines.

And finally the code will switch to 3.5MHz at beginning, to give us some
fun perspective on how much of frame time this little of machine code
can take, and how difficult it was to produce more complex games on
classic ZX Spectrum (where you would have to add all the manual drawing
of sprites and background restoring).