poking around to make a somewhat workable factory pattern

src/core/include/pw/core/vector.hpp

@@ -60,6 +60,7 @@ struct vector3_ : matrix_<3,1,T>  {
     using base_type::base_type;
     using base_type::operator = ;
 
+    vector3_() : base_type() {}
     vector3_(const base_type& m) : base_type(m) {}
     vector3_(T x_,T y_,T z_) : base_type({x_,y_,z_}) {}