Mary Barnes' comment 6

The text of the comment is:

"- [-23] Section 6.6:  All my previous concerns were addressed, except,
the Note to implementors paragraph still seems out of context - it
should be deleted or this section should be restructured so it is in
context."

- Complete rewite.  Note the additional MUST for Overlay Link protocols.
Merge pull request #190 from petithug/mary-barnes-6

Mary Barnes' comment 6