Added a way to output vec2d in an easy way

vec2d.h

@@ -2,6 +2,7 @@
 #define VEC2D_H_INCLUDED
 
 #include <cmath>
+#include <ostream>
 
 class vec2d {
   public:
@@ -67,6 +68,10 @@ public:
     }
 };
 
+static inline std::ostream& operator<<(std::ostream& os, vec2d& p) {
+    return os << '(' << p.x << ", " << p.y << ')';
+}
+
 static inline vec2d operator*(double l, const vec2d& v) {
     return vec2d{v.x * l, v.y * l};
 }