Include bytes saved in the output

[suzaku]

Sometimes, the number of bytes saved is more important to know than a percentage like "15%".

In this PR, I change the output to include the number of bytes saved so that it looks like this:

struct has size 200 (size class 208), could be 192 (size class 192), you'll save 7.69% (16 bytes) if you rearrange it to:

[suzaku]

ping @odeke-em

[suzaku]

Any luck?