OpenSystemsDevelopment / qpdf

* 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

Move ArgParser from qpdf.cc into QPDFJob.cc. It still works with
millions of public member variables, but now qpdf.cc is minimal and
just calls stable library functions.