[Cython] Documentation

[Gabriel Gellner]

At 
http://wiki.cython.org/Unsupported

optimized support for builtin types is listed, shouldn't this be in a CEP
instead? It is not really an unsupported python feature, just not a perfectly
implemented feature . . .

Also should I add a quick line that function closures are not supported, so
that all the other pages that list this as needed are more complete?

Gabriel