Indexing of "eligible" terms

[AlisdairM]

If we look at the index for "eligible" terms we see something like:

eligible
  for subsumption, 427
eligible for replacement, 306
eligible for trivial relocation, 305
eligible special member function, see special
   member function, eligible
eligible to be unblocked, 2168

Observe that "eligible" is a parent with one entry, "for subsumption", while all of the other terms of eligibility are top-level terms in their own right.

We should make this consistent, one way or the other. The simplest solution would be to promote "eligible for subsumption" to the top layer like the rest, but would the more principled approach to make all the other entries children of "eligible"?

[AlisdairM]

Waiting on editorial guidance before preparing a PR.

[jensmaurer]

We want "eligible" on the top layer and then "for subsumption" and "for replacement" and whatnot underneath.
That's much more readable.