OpenSystemsDevelopment / qpdf

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

Avoid dynamic casting.

Add optional parameter shallow. Change logic errors to runtime errors.

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

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

Update getJSON() methods and calls to them

Change object type Keyword to Operator, and place the order of the
object types in object_type_e in the same order as they are mentioned
in the PDF specification.

Note that this change only breaks backward compatibility with code
that has not yet been released.