Release 0.9.16 - Factorization, precision fixes, and documentation

This release adds prime and factorization features, improves numeric precision,
and expands simulator and user documentation.

New features

• Add IsPrime, Factors, PrevPrime and NextPrime commands
• Add MaxFactorsBits and MaxFactorIterations settings for factorization
• Add TRIGSIN command for Pythagorean identity rewrites
• Add a Unix man page and simulator documentation
• Add simulator recorder dump on F16; move demo playback to F13-F15
• Paint navigation arrows in SHOW
• Accept CR/LF line endings when reading Windows files
• Display keyboard access paths in help for commands

Bug fixes

• Fix expm1 precision loss for small arguments, including complex values
• Fix ln1p precision loss for small arguments
• Fix shift behavior after transient alpha, and support shift/xshift for transalpha
• Reset show_x and show_y when exiting SHOW
• Ensure the simulator creates the screens directory when needed
• Fix an infinity optimization regression in arithmetic
• Add missing null-dereference checks in factorization code
• Treat ^ as right-associative like on the HP50G

Enhancements

• Refactor and optimize the decimal factorization code path, with expanded tests
• Add conversion support to float and double in algebraic code
• Update to recorder v1.2.3
• Add documentation updates (DeepWiki reference, legal notice updates)
• Add build preparation for upcoming make-it-quick integration
• Welcome several new authors to the team, see AUTHORS file
• Add LEGAL-NOTICE.md about compliance with California and Colorado laws
• Add menu entries for hypot and atan2

Signed-off-by: Christophe de Dinechin christophe@dinechin.org