[docbook-apps] Can olinks replace xrefs and links?

[Denis Bradford <denis.bradford@verizon.net>]

Is there any reason not use olinks instead of xrefs and links? 
Traditionally we've used:

- xrefs for autogenerated cross-reference text, point to targets
   within the current document.

- links for authored cross-reference text, point to targets
   within the current document.

- olinks for either autogenerated or authored link text, point to
   targets in other managed documents.

But as far as I can tell, olinks seem to work just fine internally too, 
with or without generated target text. In other words, it can do 
everything that xrefs and links can do.

So my thought is, why should writers be forced to juggle four kinds of 
cross-reference elements when 2 (olinks and ulinks) will do? Another 
motivation in my case: converting an existing docset to docbook is 
simpler with only two cross-reference elements.