add support of EIP-712 signature

[AndreyMaksimkin]

implemented #323

[Iysbaera]

@AndreyMaksimkin Hey! Thank you for your contribution to the project.

As we got a grant from gitcoin foundation, we are offering a bounty to this issue in amount of 77 DAI.

We appreciate your work and ready to increase the bounty up to 300 DAI, so please apply for the bounty by the link below:
https://gitcoin.co/issue/skywinder/web3swift/323/100026048

We also kindly ask you to help us update the documentation with the information on EIP-712 usage examples.
It would be great if you can add instructions on how to use EIP-712 in web3swift library.

[CITMark]

Hello @Iysbaera & @AndreyMaksimkin I couldn't find it here or in the code, but could you tell me which version of the EIP-712 signature this is? Is it EIP712v4 by any chance? Would really appreciate any comment on this :)