Release 0.9.12 "Alive" - Return to active duty

This release focuses on simulator improvements, bug fixes, and enhanced
mathematical functionality, marking a return to active development and
maintenance after the hiatus caused by Christophe de Dinechin's move.

** New features **

* Enhanced trigonometric functions with exact angle reduction when possible
* Improved simulator graphics by smoothing the output when rescaling

** Bug fixes **

* Compute Julian day number conversion with negative Gregorian years
* Fixed crash in `lgamma` function on DM32 / DM42n platforms
* Fixed undefined symbol issue in WASM builds
* Fixed platform-specific compilation errors on Android
* Fixed incorrect simplification for `sqrt` function
* Fixed display of checksum in the `Info` box
* Fixed hang when reading CSV files containing unit objects
* Do not reorder mean and standard deviation parts in uncertain numbers
* Avoid possible null-dereference in several statistical functions

** Improvements **

* The simulator now preserves a fixed aspect ratio while resizing
* The simulator now builds cleanly on Qt5
* Added 2 new tests for Julian day number conversion
* Updated copyright year in About message
* Improved description of "Julian day number" commands in documentation
* Improved build system to select qmake6 on Arch Linux
* Show `→Num` spelling in compatibility mode
* Updated AUTHORS list
* Remove documentation for newRPL commands UDEFINE and UPURGE
* Improve implementation status section of the documentation

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