Significant progress in BitList.  Add an Ord instance that is suitable for pedigree.
It doesn't use bulk comparison, which it perhaps could in a limited way.
Add bit reversal code to BitList
Expose reverse and fromList for BitList.
Add popCount to BitList because it's another example of a good use of
bitwise ops with HW support.
Switch BitList to use unsafeShift. Add showRep to BitList.
Merge branch 'pedigree'
Perf: Replace remaining uses of the boxed Data.Concurrent.Counter (boxed IORef)
in the scheduler with Data.Atomics.Counter.

This commit should affect performance.
WIP: begin to add pedigree.  First add a per-scheduler-thread IORef.