OpenSystemsDevelopment / qpdf

This was mainly to get comments about defaults out of constructor
initializer lists where their fragile when a code formatter is being
used.

Remove test for type == /XObject in QPDFObjectHandle::isFormXObject
as type value is optional (as per spec 8.10.2).

Replace code to test for /Form in QPDFJob::shouldRemoveUnreferencedResources
with a call to isFormXObject.

If we're opening a PDF file to copy its encryption information or
attachments, its version doesn't need to influence the output version.

* Use unique_ptr in place of shared_ptr in some cases
* unique_ptr for arrays does not require a custom deleter
* use std::make_unique (c++14) where possible

All the coverage cases that used to be in qpdf.cc are now in
QPDFJob*.cc. It doesn't really matter, but better to follow the
convention of starting with the class that includes the coverage call.

All that's left now is input and output handling.

Also fix QPDFArgParser