Feature Request: show absolute before/after size (not just the diff)

Hi bloat busters, today I was using bloaty to track down binary size increases.

I got output like this:

```
FILE SIZE VM SIZE
-------------- --------------
[NEW] +1016Ki [NEW] +360Ki proto2::internal::InternalMetadataOffset::Build<>()
+56% +761Ki +62% +293Ki proto2::RepeatedPtrField<>::RepeatedPtrField()
```

I wanted to add a column showing the absolute size before. I suppose I can work it out with some maths using something like:

```
X2 = X1 + 761Ki
X2 = X1 * 1.56
X1 + 761Ki = X1 * 1.56 # set both sides equal
761Ki = X1 * 0.56 # subtract X from both sides
761Ki / 0.56 = X1
X1 = 1358
```

But it would be great if users didn't have to do this. Thank you!