Method add_block

code/chapter09/blockchain/blockchain2/core/src/blockchain.rs:25–30

(&mut self, txs: String)

    }

    pub fn add_block(&mut self, txs: String) {
        let pre_block = &self.blocks[self.blocks.len() - 1];
        let pre_hash  = pre_block.hash.clone();
        let new_block = Block::new(txs, pre_hash, self.curr_bits);
        self.blocks.push(new_block);
    }

    pub fn block_info(&self) {
        for b in self.blocks.iter() {