CHANGELOG (rc.160): add the centering rate-gate recovery on weak/low-energy data
and the SigAno anomalous signal-to-noise statistic.
CPU_DATA_ANALYSIS: describe SigAno in the merging-statistics section - its
definition, the standard PDBx mmCIF items, and why a half-set anomalous CC is not
used (complementary halves drive it negative on weak shells) - and note the
floor-independent centering-acceptance test in the space-group-determination notes.
Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>