Core N3652, Relaxing constraints on constexpr functions

The term "address constant expression" was removed but is still used in one place in clause 14; this has been reported on -core with a suggested fix, but the fix seems too large to apply editorially.

This paper interacts with core issue 1358's wording changes; I've left comments for how those interactions are resolved by this paper.

This paper uses a new "C++ 2011" macro. I wasn't sure what naming convention produces the name \CppIII for "C++ 2003", so I called the new macro \CppFIXME for now. Should it be \CppIV?

Two editorial changes here:
 -- one inserted instance of "void" is replaced by "cv void" in 3.9/10
 -- one instance of "constexpr function" is replaced by "constexpr non-static member function" in 7.1.5/8