OpenSystemsDevelopment / qpdf

This change updates all occurrences of `std::endl` to `\n` across various files for improved efficiency and consistency. It reduces unnecessary flushing of output buffers associated with `std::endl` while maintaining the same output format.

Prevent my future self or other contributors from using assert in
tests and then having that assert not do anything because of the
NDEBUG macro.

Run this:

for i in  **/*.cc **/*.c **/*.h **/*.hh; do
  clang-format < $i >| $i.new && mv $i.new $i
done

If some keys depend on others, we have to check up front since there
is no control of what order key handlers will be called. Anyway, keys
are unordered in json, so we don't want to depend on ordering.