add optional chainId in checksum

[gasolin]

evaluate if worth to support EIP-1191 (add chain id to mixed-case checksum address)
ethereum/EIPs#1121

which is already supported in several utilities
https://github.com/ethereumjs/ethereumjs-util/blob/master/src/account.ts#L134

basically it helps different EVM compatible chain users to aware to not send their token to other chain's address (via encode chain id in address)

generateAddress(addr, chainId = 1)
checkAddress(addr, chainId = 1)

[gasolin]

more discussion in PaulRBerg/ethsum#5 , close the issue