Follow cl-threads 394cd4a: processors counted on Windows
cl-threads counts the processors on Windows too, with
GetActiveProcessorCount over every processor group, so a pool's default
worker count follows them there as on Linux; elsewhere it is one worker.
The pages describe SBCL alone: the requirements, the test command, the
processor count by platform, and what cl-threads/sys takes from SBCL.
The comparisons with CCL and its join-process go.
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.
