[noise] Revision 28 draft (cosmetic)

[Trevor Perrin]

A few editorial things, haven't pushed to website yet:

https://github.com/noiseprotocol/noise_spec/blob/master/noise.md


 * Added some text to introduce "payload" earlier as a term of art.

 * More consistent use of "public_key", added explanation that
public_key encoding is specific to each set of DH functions.

 * Consistent use of "DH key pair" instead of "keypair"

 * Removed double-spacing for lists with single-line elements

 * Clarified 8.1 Pattern Validity:  The previous text mentioned you
can't "complete the handshake" unless having randomized things with
your ephemeral.  The intent was to prevent sending transport messages
without randomizing your keys, but that could be read as disallowing
the one-way handshakes.  New text is simpler and more clear that the
restriction is about *sending* encrypted data.

OLD:

After performing a DH between a remote public key and any local private key
that is not a "fresh" ephemeral private key, the local party must not send any
payloads or static public keys, nor complete the handshake, unless they have
also performed a DH between a "fresh" ephemeral private key and the remote
public key.

NEW:

After performing a DH between a remote public key and any local private key
that is not a "fresh" ephemeral private key, the local party must not send any
encrypted data unless they have also performed a DH between a "fresh" ephemeral
private key and the remote public key



Trevor