To convert the lib-intro requirements tables 29-36 into paragraphs, we don't currently have any section, and no good way to reference them.

Idea:

1. A new subsection "16.4.4.?: Basic type requirements", after [16.4.4.2, utility.arg.requirements] and before [16.4.4.3, swappable.requirements].
2. New nested subsections for each individual requirement, so that we can reference them individually (which is currently possible via the tables).

Thoughts?