Name the examples' constructors without a % prefix
The workspace's rule for names no longer marks internal functions with
a %, so the examples no longer teach it. The audio example's raw
constructor takes the free plain name, make-audio. Beside make-updater
and make-physics, which finish their objects by setting the function
that works on a chunk, the raw constructors say what they return:
make-updater-without-function and make-physics-without-chunk.
Keep the recipes' state in objects, not global variables
The program's pool, a frame's data for parallel-for, a reused job group
and a thread's stop signal now live in objects the program makes and
passes, as the workspace's rules on global state ask. Each recipe still
allocates nothing per frame, on SBCL and CCL.
