Go further with BSD license

[hartwork]

• Document change of license to 3-clause BSD license (for next release)
• Apply 3-clause BSD license where visible to the user (at runtime)
• Update "BSD 3-Clause License" to say "3-Clause BSD License" instead. Seems more suitable to humans and matches display at https://opensource.org/licenses/BSD-3-Clause (minus the "The" in the beginning).

@geissomatik this needs careful review and testing. For review, I recommend looking at each commit individually (rather than the combined diff).

[hartwork]

@geissomatik I caught something while manually testing just now, the text is cut off in practice, see below. I have an idea why that is, let's see if I can fix it…

[hartwork]

@geissomatik turns out our dear friend wsprintfA has an artificial size limit of 1024 characters on the target buffer… :smile: Looks better now, see below. Also, I returned the leading empty lines in bin_*/geiss_whatsnew.txt that seemed like a previous style choice to me, and rebased against latest main.