BTW after all this is done I'm gonna indent the entire codebase...
so `git blame` is gonna be totally broken anyway, hence my
capricious cadence of commits.
Looks like to implement the crypto opcodes I may need to switch from
rust-crypto to rust-openssl.. or implement RIPEMD-160 for rust-crypto.
In either case I will need to generalize the hash.rs stuff to support
other hashes, so I'm committing here as a checkpoint before doing all
that.