blockchain - solidity - payable 与 nonpayable

refer to:
https://medium.com/coinmonks/exploring-the-differences-between-payable-and-non-payable-functions-in-solidity-an-in-depth-d031c6ae577b

两个参数都需要调用方支付手续费（不是view, 方法)

payable: 接收 msg.value作为参数  例如转账ETH

nonpayable ： 不接收msg.value   例如调用某个合约（过程是向该合约发送0ETH）