add deterministic tests and test vectors

[david415]

other language implementations of secret-handshake should share these test vectors. this would give implementers some confidence that they've done it correctly. additionally the binary compatibility among language implementations might prove useful.

[dominictarr]

I was just thinking that actually.

If https://github.com/auditdrivencrypto/secret-handshake/blob/master/state.js was rewritten as pure functions, then we could generate extensive test vectors for each, persisted as, say, base64 strings inside json.

[david415]

yeah that sounds great... although i would think we could have deterministic tests with only rewriting bits of the tests.

[dominictarr]

done!