[wp-docs] Version specific banners for Codex

[Kaf Oseo]

Lorelle VanFossen wrote:
> Kaf, and others still thinking this way:  As long as the thinking 
> continues to be "upgrade or be deprecated", implying there is little 
> choice in the matter as you will be better off with upgrading, version 
> specific manuals are not in the offering. One manual - all versions.

I didn't say it's how I think -- it was the impression I got when I
raised the issue of what to do with 1.2.x back in February. In this
regard, Codex does not support "all versions".

-Kaf