OpenSystemsDevelopment / qpdf

This is a guess...I'm not sure exactly why there are linker issues or
how to reproduce them.

Code tidy: remove redundant calls to smart_ptrs get() method

Add QPDF::getObject to replace getObjectByObjGen and getObjectByID

For consistency with similar methods, e.g. replaceObject.

Also, make QPDFObjectHandle::isIndirect const.

Now --json-output just changes defaults. Allow output file with --json.

from "qpdf-v2" to "qpdf": [..., ...]

Add additional parameters that will be needed to call QPDF::writeJSON
in partial mode.

Code tidy : replace 0 with nullptr or true

When the schema wants a variable-length array, allow a single item as
well as allowing an array.

Remove any ambiguity around whether old or new value is being
returned.

Also, change test for QPDFObjGen::isIndirect to obj != 0.
Delete comment from commit afd35f9.

Use 'QPDFObjGen const&' instead of 'int, int' in signature.

Use QPDFObjGen::unparse where appropriate.

Change method signatures to use QPDFObjGen.
Replace QPDF_Stream::objid and generation with QPDF_Stream::og.

Change method signatures to use QPDFObjGen.
Use QPDFObjGen methods where possible.
Remove redundant QPDF::objGenToIndirect.

Change method signature to use QPDFObjGen.

Change method signature to use QPDFObjGen.

Also, revert inlining of unparse and operator << from commit 4c6640c in
order to avoid exposing QUtil.

Rather than using object id -1 to mean "don't care", use object ID 0,
and clarify the difference between that use and indication of a direct
object.

ABI breaking change

Move responsibility for creating shared pointers to objects and cloning from QPDFObjectHandle to QPDFObject.

We need to know whether pushInheritedAttributesToPage or getAllPages
have been called when generating JSON output. When reading the JSON
back in, we have to call the same methods so that object numbers will
line up properly.