Implement N3762 string_view: a non-owning reference to a string.

[Jonathan Wakely]

On 20 November 2013 14:09, Ed Smith-Rowland wrote:
>
> Here is a fix that introduces an constexpr unit length string to represent
> empty strings so that refs to empty strings don't point to the ether.

Does that static const need an out-of-class definition?