Merged the security considerations text from Ben into the master branch.
Some minor editorial corrections to the same new text.

Signed-off-by: Jouni Korhonen <jouni.korhonen@renesasmobile.com>
I goofed a bit when removing the error codes from the IANA section.

Signed-off-by: Jouni Korhonen <jouni.korhonen@renesasmobile.com>