scripts/bloat-o-meter: print percent change

This adds an additional line of output (to reduce the chances of
breaking any existing output parsers) which prints the total size before
and after and the relative difference.

  add/remove: 39/0 grow/shrink: 12408/55 up/down: 362227/-1430 (360797)
  function                                     old     new   delta
  ext4_fill_super                            10556   12590   +2034
  _fpadd_parts                                   -    1186   +1186
  ntfs_fill_super                             5340    6164    +824
  ...
  ...
  __divdf3                                     752     386    -366
  unlzma                                      3682    3274    -408
  Total: Before=5023101, After=5383898, chg 7.000000%
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Link: http://lkml.kernel.org/r/1463124110-30314-1-git-send-email-vgupta@synopsys.com
Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Michal Marek <mmarek@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>