OpenSystemsDevelopment / qpdf

Also, make QPDFObjectHandle(std::shared_ptr<QPDFObject> const&) public.

A new private overload of QPDF::makeIndirectObject breaks pikepdf's
build, so renaming function.

…ternal2 and copyObject2

copyObject2 repeats a second time what
new_obj = QPDFObjectHandle(obj->copy(true))
in shallowCopyInternal2 already did.

…ternal2 and copyObject2

Have separate versions for unsafeShallowCopy, shallowCopy and makeDirect.

* Define it even though previous experiments have shown it to be
  unnecessary since it seems like it may be necessary after all
* Add QPDF_DLL_CLASS to QPDFObjectHelper and QPDFDocumentHelper in
  case there's some future unknown reason why someone may want to have
  them and/or in case it helps with the weird
  QPDFNameTreeObjectHelper problem.

Base implementation of the buffer on std::basic_string<unsigned char>.