OpenSystemsDevelopment / qpdf

A parse error in stream data in which stream data contained a nested
object would cause a crash because qpdf was not correctly updating its
internal state. Rework the QPDF json reactor to not be sensitive to
parse errors in this way.

JSON accepts scientific notation, but PDF doesn't.

At the end of importing a JSON file, scan the object cache for reserved
objects and replace with null objects.

Allow access to private header files when defining data members.

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

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

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

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

* Replace --create-from-json=file with --json-input, which causes the
  regular input to be treated as json.
* Eliminate --to-json
* In --json=2, bring back "objects" and eliminate "objectinfo". Stream
  data is never present.
* In --json-output=2, write "qpdf-v2" with "objects" and include
  stream data.

There are no automated tests yet, but committing work so far in
preparation for some refactoring.

Also add stubs for top-level QPDF methods (createFromJSON,
updateFromJSON)