Function decode 

pub fn decode<BH, BB, E>(block: Result<BlockTuple, E>) -> Result<(BH, BB)>
where
    BH: FullBlockHeader + Value,
    BB: FullBlockBody<OmmerHeader = BH>,
    E: From<E2sError> + Error + Send + Sync + 'static,

Imports history from ERA files. Extracts a pair of [FullBlockHeader] and [FullBlockBody] from BlockTuple.