Conform to RFC2119 specification word definitions in the the hardware spec

[jonnew]

RFC2119 provides very practical definitions for the words MUST, MUST NOT, etc.

https://datatracker.ietf.org/doc/html/rfc2119

The hardware spec should conform to these words. This is related to our discussion of how to properly declare certain portions of the text as optional.

[jonnew]

This should be the last merge of V2.0. In this final PR, explanatory text and a link to the the RFC can be added to the second page of the spec. Additionally, the text should be combed for place where these words are used, or should be used.

[jonnew]

Additionally, the fact that we are doing this should be mentioned in the top level page of the hardware specification itself. Something like:

This specification uses the keywords defined in RFC2119 to indicate requirement levels.

[jonnew]

A review of the ONI specification is require to ensure that we are conforming to RFC2119.