OpenSystemsDevelopment / qpdf

When @file is used and file doesn't exist, just treat it as a normal
argument.

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

Also move tests to libtests.

Now uses QPDFOutlineDocumentHelper and QPDFOutlineObjectHelper.

Wrap an object in an array if it is not already an array.

gcc already warns for undefined variables, but this is in preparation
for Google's oss-fuzz, which builds in this way.