OpenSystemsDevelopment / qpdf

... and use it in QPDFWriter and QPDF::generateHintStream.

Also, remove redundant QPDFWriter::writeBuffer.

Also,
- use Pl_Discard when only checking whether stream is filterable
- get last char directly from output string

- Remove unnecessary QPDF_DLLs
- make deleted constructors public
- move some comments to support tooltips
- modernise some constructors and destructors
- change some member shared pointers to unique pointers

Except for virtual functions to avoid the need for users to update code.

Also, uninitialize QPDFWriter::Members members.

Use string_view parameters and call pipeline write methods directly.

These markers are being added for nested classes that are already
marked with QPDF_DLL_CLASS. They don't make any different on Linux,
but they matter on Windows.

(patrepl and cleanpatch are my own utilities)

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

Run this:

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