Currently we have fn simple_hash_from_byte_slices(byte_slices: &[&[u8]]) -> Hash

But this leads to some complexities in the few places it's so far used:

• https://github.com/interchainio/tendermint-rs/blob/10a3026cfbd4ab333752d344645a4f07ecdc29f7/tendermint/src/validator.rs#L23-L35
• https://github.com/interchainio/tendermint-rs/pull/36/files#diff-a1644bb72a1c83c54d82738ef71ce095R126 (ie. the need for a separate variable followed by as_slice would go away)