Consider morph::vvec<morph::vec<C, 2>> as container in morph::Grid

[sebjameswml]

Rather than using

        //! Two vector structures that contains the coords for this grid. v_x is a vector of the x coordinates
        morph::vvec<C> v_x;
        //! v_y is a vector of the y coordinates
        morph::vvec<C> v_y;

Instead consider

        morph::vvec<morph::vec<C, 2>> v_coords;