Update for 2.6.10
2.6.10: will be tagged as "sbcl-2.6.10"
Fill in some more NEWS from browsing git log
Add NEWS for launchpad bugs and for changes acknowledging a report
NEWS item for printing subnormal floats
Revert (DECLARE VALUES) changes for now
Print subnormal floats with their shortest digits
Update to Unicode 18.0.0