Obsolete documentation

[Akim Demaille]

The current CVS documentation mixes in the text body the documentation
of recent and obsolete macros.  I'm in favor of moving the obsolete
macros documentation into the chapter `Old Names', renamed as
`Obsolete Macros'.  Plain lexicographic order seems fine there, no
need to introduce new sections, but maybe we should?

I'm ready to do that.  I'll leave a few @ref where needed.

        Akim