[noise] Small protocol detail

[Trevor Perrin]

On Mon, Apr 4, 2016 at 12:23 AM, Alex <alex at centromere.net> wrote:
> Patterns using semi-ephemeral keys were removed, yet the following
> statement in section 8 remains:
>
>> The tokens "s" and/or "e" inside the parentheses would indicate that
>> the initiator is initialized with static and/or ephemeral key pairs.
>> The tokens "rs" and/or "re" would indicate the same thing for the
>> responder.

The pattern language can still describe those patterns, there's just
no examples of them in the current document, since:
(1) they're probably more complicated and less useful than just
encrypting to the static public key
(2) lifetimes of semi-ephemeral keys are more complicated to discuss
(3) in some cases they'd benefit from signatures (signing the
ephemeral) which Noise doesn't have yet

But I think we might as well leave support for them in the pattern
language, so they're easy to describe and support if people want them.
Make sense?

Trevor