Method transfer

chain/src/account.rs:82–87

(&mut self, from: &Account, to: &Account, amount: U256)

    }

    pub(crate) fn transfer(&mut self, from: &Account, to: &Account, amount: U256) -> Result<()> {
        self.subtract_account_balance(from, amount)?;
        self.add_account_balance(to, amount)?;

        Ok(())
    }

    // TODO(ddimaria): remove
    pub(crate) fn update_nonce(&mut self, key: &Account, nonce: U256) -> Result<U256> {