OpenSystemsDevelopment / qpdf

I decided these were confusing and inconsistent with how JSON works.
They muddle the API rather than improving it.

Call the parent container's item method before calling the child
item's start method so we can easily know the current nesting level
when nested items are added.

Update getJSON() methods and calls to them

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.

Bidirectional base64; will be used by JSON v2.

Where not possible, use "auto" to get the iterator type.

Editorial note: I have avoid this change for a long time because of
not wanting to make gratuitous changes to version history, which can
obscure when certain changes were made, but with having recently
touched every single file to apply automatic code formatting and with
making several broad changes to the API, I decided it was time to take
the plunge and get rid of the older (pre-C++11) verbose iterator
syntax. The new code is just easier to read and understand, and in
many cases, it will be more effecient as fewer temporary copies are
being made.

m-holger, if you're reading, you can see that I've finally come
around. :-)

Change .clang-format and commit automated changes from a fresh run of
format-code

Increase to POINTERHOLDER_TRANSITION=4

Increase to POINTERHOLDER_TRANSITION=3

patrepl s/PointerHolder/std::shared_ptr/g **/*.cc **/*.hh
patrepl s/make_pointer_holder/std::make_shared/g **/*.cc
patrepl s/make_array_pointer_holder/QUtil::make_shared_array/g **/*.cc
patrepl s,qpdf/std::shared_ptr,qpdf/PointerHolder, **/*.cc **/*.hh
git restore include/qpdf/PointerHolder.hh
git restore libtests/pointer_holder.cc
cleanpatch
./format-code

Run this:

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

It's better to just make it a .hh file to reduce confusion.