Update text and examples regarding the fetching of TDs

[JKRhb]

In the current Editor's draft, there are a couple of leftovers from previous versions where the requestThingDescription had not been introduced yet. This PR updates the text, incorporates the latest changes, and also removes an outdated appendix that explains why there is no fetch method anymore (which has now de facto been reintroduced). Maybe some text regarding the validation of TDs could be added/moved elsewhere, though.

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Preview | Diff

[danielpeintner]

Content-wise LGTM

see comment below about quotes...

[relu91]

Call 04/12/2023:

• @zolkis don't agree to remove fetch from the examples. It is still valid, since the convenience function does not cover all the use cases of WoT, which might need to use e.g. HTTP options. We still have to mention it and we need to explain that it is possible to fetch, and make examples to highlight when you need fetch and the convenience function.
• @danielpeintner best practice is to use the new method because they get some validation.
• @JKRhb fetch and HTTP requests are still mentioned in the text, it could cover the comments above.

Group decision: rework the rationale removed by mentioning the use cases for fetch and requestThingDescription. Double check mentioning of fetch or HTTP requesting in the whole spec text.

[zolkis]

IMHO we need to keep the (reworked) fetch and validate section.

[zolkis]

Some relevant historical discussions, please check:
#78
#162
#216

[relu91]

I think it is better to change it into an assertion (?)

[relu91]

Call 11/12

• @ashimura Having the appendix is fine but we should explain its purpose
• @zolkis we can introduce it in the section about requestThingDescription
• @danielpeintner matching spec sections with rationale sections makes sense. I would do this in general (we should have already probably worth checking)

[zolkis]

From my part, we can deal with improving the section 5 vs appendix A in a new issue and merge this PR.

[relu91]

Call 15/01:

• @relu91 merging PR