Preliminary implementation of json mode
Preliminary implementation of json mode

The json mode implemented in this commit is not the final version, or
are the command line arguments used to invoke it.

jberkenbilt/qpdf,qpdf/qpdf,qpdf/qpdf,qpdf/qpdf,jberkenbilt/qpdf,qpdf/qpdf,jberkenbilt/qpdf,jberkenbilt/qpdf,jberkenbilt/qpdf,qpdf/qpdf