Replaced throw() with BOOST_NOEXCEPT_OR_NOTHROW

With throw(), Visual Studio 2017 emitted a warning "C26439 SPECIAL_NOEXCEPT". Reproducible at least if code analysis was set to level: "Microsoft Native Recommended Rules".

https://docs.microsoft.com/en-us/visualstudio/code-quality/c26439?view=vs-2017

example/example_io.cpp

@@ -35,14 +35,14 @@ error: //Base for all exception objects we throw.
     public:
 
     char const *
-    what() const throw()
+    what() const BOOST_NOEXCEPT_OR_NOTHROW
         {
         return "example_io error";
         }
 
     protected:
 
-    ~error() throw()
+    ~error() BOOST_NOEXCEPT_OR_NOTHROW
         {
         }
     };