Making it clear that FINAL must be processed for all frame types, even unsupported ones.
Removing redundant usage-type details from the streams section.
Taking a stab at defining 'peer'.
Clarifying half-close for unidirectional streams.
Clarifying the stream ID for ping.  Now that this is a stream ID, you can't use a non-zero ID (can't guarantee that the stream is open for the mandatory PONG).