Checksums added for all 6-piece tables. Correctness has been verified by
comparing with the tables generated by Jean-Francois Romang.
Total size of WDL tables in README lowered from 68.3 GB to 68.2 GB. This
is due to a compression optimisation that sometimes failed to kick in
because of a bug that was corrected only after I generated my own tables.
The optimisation reduced 55 affected WDL tables by in total 118.5 MB.