OpenSystemsDevelopment / qpdf

Add new method QPDF::newReserved()

Add new convenience class QPDFObjGen::Guard

Allow access to private header files when defining data members.

A new private overload of QPDF::makeIndirectObject breaks pikepdf's
build, so renaming function.

Removing an element from a set with iterator is constant time, and
std::set specifies that other operations on the set do not invalidate
existing iterators.

QPDFValueProxy wasn't a good name for it. We decided the evil of
having the header file be named QPDFObject_private.hh was less than
the evil of having the class be named something other than what it
should have been named.

This is in preparation for restoring a QPDFObject.hh to ease the
transition on qpdf_object_type_e.

This commit was created by
* Renaming QPDFObject.cc and QPDFObject.hh
* Replacing QPDFObject\b with QPDFValueProxy (where \b is word
  boundary)
* Running format-code
* Manually resorting files in libqpdf/CMakeLists.txt
* Manually refilling the comment in QPDF.hh near class Resolver

Tidy QPDF::getAllPagesInternal and QPDF::pushInheritedAttributesToPageInternal