This shows that there's too much padding because we pad based on
number of bytes.
I had to reduce the path names for the file names not to get too long
for my file system.
We can still crash on terminals that are less than 4 characters wide
(maybe it doesn't matter if we do because the user can't tell the
crash report from a diffstat in such a terminal?). This patch fixes
the crash.
We would run into a panic due to "attempt to subtract with overflow"
if the path was long. This patch fixes that and adds tests showing the
current behavior when there are long paths and/or large diffs.
I've extracted the `builtin_log_root` template for users to customize the
default templates without fully overriding them, for example I would remove
the change_id/commit_id for myself - and we discussed in Discord that leaving
those makes sense for the user to be reminded/teached that the root commit has
a change id made from z's.
Empty files can be confusing in diff output. For example:
```
Added regular file file1:
Added regular file file2:
1: foo
```
This commit adds an "(empty)" placeholder instead. Since it's not
colored, and doesn't have line numbers, it will hopefully not be
mistaken for a file with the contents "(empty)".
