Add the ability to generate SHA512 hashes of passwords for use in ezproxy.usr.
 
Sample use from a command prompt or shell to generate a SHA512 hash:

ezproxy SHA512 testing
$021NGKBG$FTRoPxyZ1S2O2bJ5qRtlXcI/tKPXZRoaQojBFZKWOif0g5Fionk07Bo13fN2+a/kmL8w80VumtcA2m1ENEiT2A


Sample use in ezproxy.usr for this password: 

someuser::SHA512=$021NGKBG$FTRoPxyZ1S2O2bJ5qRtlXcI/tKPXZRoaQojBFZKWOif0g5Fionk07Bo13fN2+a/kmL8w80VumtcA2m1ENEiT2A