OpenSystemsDevelopment / qpdf

This is so it will fit on one line after a qtest upgrade allows us to
split lines.

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

The PDF spec only allows UTF-16BE, but most readers seem to accept
UTF-16LE as well, so now qpdf does too.

This was unintended behavior that was added back for backward
compatibility. It is intentionally undocumented.

There are codepoints in PDFDoc that are not valid UTF-8 but map to
valid UTF-8. We were handling those correctly with bidirectional
mapping.

However, if those same code points appeared in UTF-8, where they have
no meaning, they were left as fixed points when converting to PDFDoc,
where they do have meaning. This change recognizes them as errors.

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.

This comment expands all tabs using an 8-character tab-width. You
should ignore this commit when using git blame or use git blame -w.

In the early days, I used to use tabs where possible for indentation,
since emacs did this automatically. In recent years, I have switched
to only using spaces, which means qpdf source code has been a mixture
of spaces and tabs. I have avoided cleaning this up because of not
wanting gratuitous whitespaces change to cloud the output of git
blame, but I changed my mind after discussing with users who view qpdf
source code in editors/IDEs that have other tab widths by default and
in light of the fact that I am planning to start applying automatic
code formatting soon.

This will be able to be replaced with QUtil::make_shared_array

Replace PointerHolder arrays wherever it can be done without breaking ABI.

Create the typedefs directly in iterators rather than deriving from
the deprecated std::iterator class.

* 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

None of these are in the public API.