Improve the summary (formerly text) report

[aantron]

It currently looks like this:

Coverage summary: 1368/1728 (79.17%)
File 'bisect_ppx/src/common/bisect_common.ml': 123/153 (80.39%)
File 'bisect_ppx/src/ppx/exclude.ml': none
File 'bisect_ppx/src/ppx/exclude_lexer.ml': 28/77 (36.36%)
File 'bisect_ppx/src/ppx/exclude_parser.ml': 38/53 (71.70%)
File 'bisect_ppx/src/ppx/exclusions.ml': 36/42 (85.71%)
File 'bisect_ppx/src/ppx/instrument.ml': 395/435 (90.80%)
File 'bisect_ppx/src/ppx/register.ml': 13/23 (56.52%)
File 'bisect_ppx/src/report/assets.ml': none
File 'bisect_ppx/src/report/report.ml': 357/452 (78.98%)
File 'bisect_ppx/src/report/report_coveralls.ml': 84/93 (90.32%)
File 'bisect_ppx/src/report/report_csv.ml': 10/10 (100.00%)
File 'bisect_ppx/src/report/report_dump.ml': 8/8 (100.00%)
File 'bisect_ppx/src/report/report_generic.ml': 44/47 (93.62%)
File 'bisect_ppx/src/report/report_html.ml': 142/164 (86.59%)
File 'bisect_ppx/src/report/report_text.ml': 17/20 (85.00%)
File 'bisect_ppx/src/report/report_utils.ml': 55/86 (63.95%)
File 'bisect_ppx/src/runtime/native/runtime.ml': 18/65 (27.69%)

The numbers should be on the left, and everything should be nicely aligned. The summary line is probably best shown at the bottom.

[aantron]

$ bisect-ppx-report summary
Coverage: 1382/1766 (78.26%)

$ bisect-ppx-report summary --per-file
 80.39 %    123/153    bisect_ppx/src/common/bisect_common.ml
  0.00 %      0/0      bisect_ppx/src/ppx/exclude.ml
 36.36 %     28/77     bisect_ppx/src/ppx/exclude_lexer.ml
 71.70 %     38/53     bisect_ppx/src/ppx/exclude_parser.ml
 85.71 %     36/42     bisect_ppx/src/ppx/exclusions.ml
 90.80 %    395/435    bisect_ppx/src/ppx/instrument.ml
 56.52 %     13/23     bisect_ppx/src/ppx/register.ml
  0.00 %      0/0      bisect_ppx/src/report/assets.ml
 78.59 %    356/453    bisect_ppx/src/report/report.ml
 90.32 %     84/93     bisect_ppx/src/report/report_coveralls.ml
100.00 %     10/10     bisect_ppx/src/report/report_csv.ml
100.00 %      8/8      bisect_ppx/src/report/report_dump.ml
 91.49 %     43/47     bisect_ppx/src/report/report_generic.ml
 86.59 %    142/164    bisect_ppx/src/report/report_html.ml
 57.89 %     33/57     bisect_ppx/src/report/report_text.ml
 63.95 %     55/86     bisect_ppx/src/report/report_utils.ml
 27.69 %     18/65     bisect_ppx/src/runtime/native/runtime.ml
 78.26 %   1382/1766   Project coverage