OpenSystemsDevelopment / qpdf

...and include ObjectHandle.hh first in QPDFObjectHandle so there is
at least one place (other than check_abi get-sizes) that includes it
first.

Update release notes and reverse making QPDFObjectHandle final

and delay to qpdf 13 to give users notice of the change.

- 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

Move all stream-specific methods to new class qpdf::Stream

Move all array-specific methods to new class qpdf::Array.

Move all dictionary specific methods to BaseDictionary. Create new subclass
Dictionary to allow QPDFObjectHandle to access the moved methods.

The new class is only usable as base classes and does not support direct
instantiation or upcasting.

Add operators to convert to bool, QPDFObjectHandle and QPDFObjGen.

Derive QPDFObjectHandle from BaseHandle and make final.

This improves indentation of long strings. This commit also fixes some
trailing whitespace in ChangeLog.

Create an alternative to getJSON to allow an object handle to be written as JSON without the overhead of creating a JSON object.

Add new convenience class QPDFObjGen::Guard

Also, add const overload of QPDFObjectHandle::getObj

Add temporary clone of SparseOHArray  to implement non-sparse mode.

This reverts commit 56c923d1096b0317d978bdadeb44e8198053286c.

This commit breaks pikepdf.