Fix: RFC 2119 link

[ax3l]

The link to IETF RFC 2119 is broken.

This adds a new link and changes the spelling of keywords to lowercase.

[s9105947]

Is there a specific reason to break with the corresponding BCP 14, which consists of RFC 2119 (keyword definition) + the 2017 update RFC 8174 (spelling clarification) which demand to always use ALLCAPS?

Personally I totally missed that the lower-case keywords are intended to follow RFC 2119 when first skimming the standard -- allthough I suppose the allcaps might be confusing when unfamiliar.

[ax3l]

Yes, all-caps is just too weird to read and thus we never did that. Thus we re-define the keywords to lowercase now, otherwise same naming as indicated.

This whole definition is just a clarification, because many non-native (and some native) English speakers do not immediately see the difference between must and shall/should. This RFC nicely resolves this by clearly defining the meaning and difference/equivalence of such qualifiers.

[ax3l]

@s9105947 is it ok if you add your name & affiliation to https://github.com/settings please ? :)
It's a bit hard otherwise for us to keep track who we email and chat on GitHub with 🙂