Improved display of output

The output of matrices, vectors, and repeated composition has been improved. Example: compute a Taylor series expansion for an unknown function

    > s := taylor(f(x),x=0,4);

                                  (2)        2        (3)        3      4
     s := f(0) + D(f)(0) x + 1/2 D   (f)(0) x  + 1/6 D   (f)(0) x  + O(x )

    > linalg[vector]( 4, i -> coeff(s,x,i-1) );

                                     (2)             (3)
               [ f(0), D(f)(0), 1/2 D   (f)(0), 1/6 D   (f)(0) ]