added zero spline

include/spline/bezier_curve.h

@@ -301,7 +301,13 @@ struct bezier_curve : public curve_abc<Time, Numeric, Dim, Safe, Point>
     private:
     t_point_t  pts_;
 
-    //storing bernstein polynoms, even in low dimension
+    public:
+    static bezier_curve_t zero(const time_t T=1.)
+    {
+        std::vector<point_t> ts;
+        ts.push_back(point_t::Zero());
+        return bezier_curve_t(ts.begin(), ts.end(),T);
+    }
 };
 }
 #endif //_CLASS_BEZIERCURVE