cmd/multitool: Add sha512 and sha512alt subcommands
cmd/multitool: Add sha512 and sha512alt subcommands



Closes chain/chainprv#1208.
Reviewers: da39a3ee5e6b4b0d3255bfef95601890afd80709@erykwalder




chain/chain,chain/chain,chain/chain,chain/chain,chain/chain,chain/chain