##### const_buffer::const_buffer (4 of 4 overloads)

Construct a buffer from a span of bytes.

    template<
        template< typename, std::size_t > class Span,
        typename T,
        std::size_t Extent>
    const_buffer(
        const Span< T, Extent > & span,
        constraint_t< sizeof(T)==1, defaulted_constraint >  = defaulted_constraint(),
        constraint_t< is_same< decltype(span.subspan(0, 0)), Span< T, static_cast< std::size_t >(-1)> >::value, defaulted_constraint >  = defaulted_constraint());