Use the latest ReSpec functionalites

[relu91]

In scripting API recently we fixed a bunch of issues related to how we cross-site different parts of our spec and 3rd parties specifications. We should cross-check all the documents and verify that we use ReSpec correctly.

1. https://github.com/w3c/respec/wiki/xref
2. https://github.com/w3c/respec/wiki/Auto-linking-external-references

Tool for references: https://respec.org/xref/.

[relu91]

Tool for references: https://respec.org/xref/.

It seems that our terms (e.g. I couldn't find Thing Description) are not listed there, should we add them?

On the other hand, you can find our terms here: https://respec.org/specref/

[egekorkan]

Also see #1019