Disable macro max in Windows. Implement move ctors in string_span for VS2013. Remove redundant pragma warning pop for VS2013.

include/string_span.h

@@ -235,13 +235,28 @@ public:
     constexpr basic_string_span(const basic_string_span& other) = default;
 
     // move
+#ifdef GSL_MSVC_NO_SUPPORT_FOR_MOVE_CTOR_DEFAULT
+    constexpr basic_string_span(basic_string_span&& other)
+		: span_(std::move(other.span_))
+	{
+	}
+#else
     constexpr basic_string_span(basic_string_span&& other) = default;
+#endif
 
     // assign
     constexpr basic_string_span& operator=(const basic_string_span& other) = default;
 
     // move assign
+#ifdef GSL_MSVC_NO_SUPPORT_FOR_MOVE_CTOR_DEFAULT
+    constexpr basic_string_span& operator=(basic_string_span&& other)
+	{
+		span_ = std::move(other.span_);
+		return *this;
+	}
+#else
     constexpr basic_string_span& operator=(basic_string_span&& other) = default;
+#endif
 
     // from nullptr and length
     constexpr basic_string_span(std::nullptr_t ptr, size_type length) noexcept
@@ -561,8 +576,6 @@ bool operator>=(const gsl::basic_string_span<CharT, Extent>& one, const gsl::bas
 
 #if _MSC_VER <= 1800
 
-#pragma warning(pop)
-
 #ifndef GSL_THROW_ON_CONTRACT_VIOLATION
 #undef noexcept
 #pragma pop_macro("noexcept")