OpenSystemsDevelopment / qpdf

Set parsed offset at the same time as setting description.

Modify QPDFParser::parse to call QPDF::getObject instead.

Also remove no-longer-needed #include

Avoid creating new null objects that later will be discarded and made
implicit.

Part of #729

Part of #729

Part of #729

Replace SparseOHArray with std::vector<QPDFObjectHandle>.

Part of #729

Part of #729

Part of #729

Part of #729