OpenSystemsDevelopment / qpdf

This makes the code simpler than having to create a buffer of a fixed
size and copy the string to it.

This rework makes xref reconstruction run much faster and use much
less memory.

With QPDF allowing integers to contain 64-bit quantities, this change
is necessary to be able to linearize files whose sizes might be larger
than 10 digits.

This makes it possible to store offsets that are larger than 2 GB in
the trailer dictionary.

This just makes it safer to pull up this file in an editor.

Also updated pdf_from_scratch test driver to use the new factories,
and made some cosmetic improvements and documentation updates for the
emptyPDF() method.

off_t is used internally only when needed to talk to standard
libraries.  This requires that the "long long" type be supported by
the compiler.

Thanks Tobias Hoffmann for noticing the error.

Split optimizePagesTree into a simpler top-level routine and a
recursive internal routine.

Added methods to append to arrays, insert items into arrays, and
replace array contents with a vector of items.

Significantly improve the code's use of off_t for file offsets, size_t
for memory sizes, and integer types in cases where there has to be
compatibility with external interfaces.  Rework sections of the code
that would have prevented qpdf from working on files larger than 2 (or
maybe 4) GB in size.

For ELF systems, turn on versioned symbols by default, and add a
configure option to enable or disable them.

pcre_info -> pcre_fullinfo.  Closes issue 3489349.  Thanks Tim Harder.