* Use CMake's built-in timestamp formatting.
It notably honors SOURCE_DATE_EPOCH if set, making for reproducible
output. For even better reproducibility, use UTC. (Unlike the date
command's output, the result is already always in English.) Extend
this approach to the book, introducing appropriately formatted
PDF_DATE and TODAY variables for its PDF metadata and title page
respectively and making make_pdf configurable.
Under the traditional build system, don't attempt to handle
SOURCE_DATE_EPOCH because date's portable interface is too limited,
just supply PDF_DATE and TODAY values corresponding to the current
date (and time zone) and use the C (English) locale for month names
and abbreviations.
* Fix missing parts and a syntax error in documentation/Makefile
- documentation/Makefile:
- add make_pdf to target 'clean'
- add make_pdf to dependencies of 'refman.pdf'
- add missing quotes to `date` command
- documentation/.gitignore: add make_pdf
---------
Co-authored-by: Albrecht Schlosser <albrechts.fltk@online.de>
