API changes

Between beta 4 and 1.0 the API for creating mail has changed. MutableMail has been replaced by PostOffice which is a factory for creating encrypted mail. There's no longer any need to manually increment the sequence number as that's done for you. Instead make sure to only have one instance per sender key and topic. This allows the enclave to check for dropped or reordered mail. Mail.decrypt and EnclaveInstanceInfo.decryptMail have been replaced by PostOffice.decryptMail. Decrypt any response mail using the same post office instance that created the request.

Inside the enclave Enclave.createMail has been replaced by Enclave.postOffice which returns a cached post office for the destination and topic. This means you don't need to manage post office instances inside the enclave as you do in the client.

The routing hint parameter in Enclave.receiveMail has been moved to the end to make the method signature consistent with EnclaveHost.deliverMail.