Multisignature support
Hello,

Thanks for the great work you’ve done there.

As you may know, monero v0.13.0.4 has finally stabilized M-N multisig of monero.

The JSON RPC has `create_wallet, prepare_multisig, make_multisig, finalize_multisig` to create a multisignature wallet.

Can you implement that feature to this wonderful library? I would like to help, but the creation is too complicated for the api to expose the methods clean.

Thanks.