ref: use mode init parameter again

[karrui]

This PR builds on #34, #36, #38 but removed the publicKey parameter after extensive discussion with @liangyuanruo

Reasons for removal

1. Allowing users to update their public keys as an environment variable wouldn't have worked seamlessly anyways in the event of a private key leak, and would require users to be disseminated new public keys and to use the new public keys.

Would be easier to actually update the sdk and make users update??

[karrui]

@liangyuanruo i've tested it on local with this commit, all works as they should.