Add alt code for 2001/kev - arrow key support

Since arrow keys can be more natural than other keys like the program's
',' and '.' for movement I added a version which lets you use arrow keys
instead. One player could use the ',' and the other '.' or both can play
with the same, whichever they pick.

I also slowed down the speed of the ball as it moved very fast
considering the slow speed the paddle moves. The README.md shows how to
reset it or change the value via make.

Updated .gitignore.

2001/kev/.gitignore

@@ -1 +1,2 @@
 kev
+kev.alt