[wwwdocs] Additional C++ entries in changes.html

[Paolo Carlini]

Jonathan Lennox wrote:

> Out of curiosity, what are the known areas where G++ is still
> non-conformant?

Perhaps "non-trivial covariant returns for varadic virtual function"?

(don't ask me what does this exactly mean, though ;) ;)

I concur, it would be nice to have a c++98status.html and also a
c++03status.html!

(Giovanni would enjoy working on the latter, I guess!)

Paolo.