copy method
Implementation
Matrix4 copy(Matrix4 m) {
var te = elements;
var me = m.elements;
te[0] = me[0];
te[1] = me[1];
te[2] = me[2];
te[3] = me[3];
te[4] = me[4];
te[5] = me[5];
te[6] = me[6];
te[7] = me[7];
te[8] = me[8];
te[9] = me[9];
te[10] = me[10];
te[11] = me[11];
te[12] = me[12];
te[13] = me[13];
te[14] = me[14];
te[15] = me[15];
return this;
}