Nov 1, 2018 - 1.40:
    New interpreters:
        Added CPython 3.7
        Added pypy 5.10.0 and pypy3 5.10.0
        Added pypy 6.0.0 and pypy3 6.0.0

    No longer supported interpreters:
        Jython 2.7.0; it's legacy python and had a bad bug
        Python 2.5 and 2.6

    Security fixes:
        Create save directory (via --init-savedir) with mode 700, owner=rwx, group=---, world=---

    Bug fixes:
        Fixed a rare traceback when a symlink disappears
        Fixed some inconsistent returns
        Verbose output no longer gives traceback for nonunicode filenames on Python 3

    Minor improvements:
        Progress moderate when on a tty
        Put rolling_checksum_pyx_mod in $prefix/lib/backshift/. not site-packages directory
        Improved some error messages a little.
        Tests no longer require Python 3
        ./configure script smarter about what it recommends for performance