Improve report format

Test plan: Generate this beautiful report:

                                          ExerciseBiasDim. 1
                 area-and-circumference-of-circles0.15270.1627
                            equation_of_an_ellipse0.23900.0599
                      two-sided-limits-from-graphs0.33920.0654
                                     subtraction_10.34540.1430
                                   scaling_vectors0.38140.1886
               dividing_polynomials_by_binomials_10.39910.3312
                               area_of_triangles_10.42230.0746
                                          volume_10.5618-0.0479
                understanding_decimals_place_value0.86950.0884
understanding-multiplying-fractions-and-whole-numbers0.97940.1425