Log Message:
Update to 6.0.0

Changelog:
2015-11-10  Jay Berkenbilt  <ejb@ql.org>

        * 6.0.0: release

        * No changes from 5.2.0. The 5.2.0 release broke binary
        compatibility and was withdrawn.

2015-10-31  Jay Berkenbilt  <ejb@ql.org>

        * 5.2.0: release

        * libqpdf/QPDF.cc (read_xrefTable): Be tolerant of some malformed
        xref tables that don't have the required trailing space after each
        line.

2015-10-29  Jay Berkenbilt  <ejb@ql.org>

        * Implement QPDFWriter::setDeterministicID and --deterministic-id
        commandline-flag to qpdf to request generation of a deterministic
        /ID for non-encrypted files.