message: try delegate constructor
diff: @@ -132,13 +132,21 @@ namespace RINGMesh {
  * Logger::err( "Exception", e.what() );
  * }
  */
  - class RINGMESH_API RINGMeshException {
  + class RINGMESH_API RINGMeshException: public std::runtime_error {
  public:
  +
  + RINGMeshException()
  + : message_( "" )
  + {
  +
  + }
  template< typename ...Args >
  explicit RINGMeshException( std::string category, const Args& ...messages )
  - : category_( std::move( category ) )
  + :
  + RINGMeshException(),
  + std::exception( string_concatener( messages... ) ),
  + category_( std::move( category ) )
  {
  - message_ = string_concatener( messages... );
  }
  virtual ~RINGMeshException() throw()
  {
  @@ -149,11 +157,6 @@ namespace RINGMesh {
  return category_;
  }
  - const std::string& what() const
  - {
  - return message_;
  - }
  -
  private:
  std::string& string_concatener()
  {
  @@ -163,7 +166,7 @@ namespace RINGMesh {
  template< class A0, class ...Args >
  std::string& string_concatener( const A0& a0, const Args& ...args )
  {
  - message_ += GEO::String::to_string( a0 );
  + message_ +=std::to_string( a0 );
  return string_concatener( args... );
  }
  protected:
  