OpenSystemsDevelopment / qpdf

- 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

Run this:

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