OpenSystemsDevelopment / qpdf

This is a massive rewrite of the help text and cli.rst section of the
manual. All command-line flags now have their own help and are
specifically index. qpdf --help is completely redone.

Handle optional choices in addition to required choices. Refactor the
way help options are added to completion to make it work with optional
help choices.

Converted ResourceFinder to ParserCallbacks so we can better detect
the name that precedes various operators and use the operators to sort
the names into resource types. This enables us to be smarter about
detecting unreferenced resources in pages and also sets the stage for
reconciling differences in /DR across documents.

Keep a std::pair internal to the iterators so that operator* can
return a reference and operator-> can work, and each can work without
copying pairs of objects around.

Add constructors that take a QPDF object so we can issue warnings and
create new indirect objects.

Create a computationally and memory efficient implementation of name
and number trees that does binary searches as intended by the data
structure rather than loading into a map, which can use a great deal
of memory and can be very slow.

Refactor QPDF_Stream to use stream filter classes to handle supported
stream filters as well.

OPENSSL_IS_BORINGSSL is not actually set by configure, so it will be
undefined until a BoringSSL header is included.  Hence the #ifdef logic
in QPDFCrypto_openssl.h would usually never apply.

This still worked because evp.h transitively included BoringSSL's
cipher.h and digest.h, but the latter are the correct (documented)
headers.

By re-ordering the includes, we can ensure the macro is defined when we
use it.

Also: fix case in the header guards.

Use autoconf rather than ifdefs to determine what format string to use
for long long.

Fixes qpdf/qpdf#417

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

This was added in C++11.

Thanks to Zdenek Dohnal <zdohnal@redhat.com> for contributing the code
used for the gnutls crypto provider.