POSIX msgfmt and newlines in strings

[Bruno Haible]

https://posix.rhansen.org/p/gettext_draft
Line 1067

"Unlike shell command language strings, double-quoted strings in dot-po files
cannot contain a literal <newline> character."

Issue: This sentence should be part of the specification of the dot-po file 
format.

Suggestion: Move this sentence from the APPLICATION USAGE section to the
EXTENDED DESCRIPTION section.