#13 please add sha256 hash

[Charles Evans]

I would like to use sha256 hashing for verification,
and I prefer to keep using your excellent program.
As you likely know, any verification that must be reliable over the long term must be strong enough to
withstand future threats, not just current ones.
Moore's law is the best-case, not the worst-case scenario.
Since sha-1 has been shown to have some weaknesses, government use of sha-1 has been restricted somewhat.
Debian now has sha-256 hashes on all deb packages
(see apt-cache search --full cfv)
Thanks again.