OpenSystemsDevelopment / qpdf

Warn if catalog type entry is invalid (fixes #810)

Improve --optimize-images to find images nested within XObjects

Also, change QPDFJob to use unique_ptr<QPDF> instead of shared pointers.

Also, inline method and add optional parameter error_msg.

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

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

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

Use QPDFObjGen::unparse where appropriate.

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

Remove redundant variables pages and next.

This includes the output PDF, streams from --show-object and
attachments from --save-attachment. This also enables --verbose and
--progress to work with saving to stdout.