Currently there's only one numeric column, and that's the file size, so it gets
special treatment.
I was originally going to have a folder file size field be filled up with '-'s
as far as it could go, leaving it entirely up to the column how its field gets
formatted. But then I saw just one '-' working just fine, so I left it like
that. In the first try, columns could do anything they want when padding a
string (including changing the padding character or just changing it entirely),
but now there's no point.
I'm copying ls here because we don't really need the 'B' for bytes to be
listed every time. I think it looks better the new way. Unlike ls, don't
list directory sizes, because I've never found the pseudo-sizes they get
given at all useful.
Also, fix a bug where aligning columns didn't work when the number of
format characters (like '\x1B' and '[') were different between each
line.
Also, reverse the way columns are rendered: before, a column took a stat and a name to render; now, a file takes a column type to render. This means that most of the File data/methods can be private.
