OpenSystemsDevelopment / qpdf

When possible, use `for (auto&` or `for (auto const&` when iterating
using C++-11 style iterators.

Also switch to colon-style iteration in some cases. Thanks to Dean
Scarff for drawing this to my attention after detecting some
unnecessary copies with
https://clang.llvm.org/extra/clang-tidy/checks/performance-for-range-copy.html

This uses C++-11 thread-safe static initializers now.

Fixes qpdf/qpdf#417

StreamDataProvider::provideStreamData now has a rich enough API for it
to effectively proxy to pipeStreamData.

Fixes qpdf/qpdf#419

This was being saved until we had to break ABI.

This was added in C++11.

If a page contains a form XObject, also filter the form XObject and
remove its unreferenced resources.

Refactor removeUnreferencedResources to prepare for filtering form
XObjects.

fix-qdf assumes there is exactly one XRef stream and that it is at the
end of the file.

If the value of /CS in the inline image dictionary was is key in the
page's /Resource -> /ColorSpace dictionary, properly resolve it by
referencing the proper colorspace, and not just the name, in the
external image dictionary.

Fix is based on guidance
https://support.microsoft.com/en-us/help/238187/cryptacquirecontext-use-and-troubleshooting
and is the proper fix for #285/#286