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.

They get computed often enough for this to be worthwhile, and I have plans for using the extension even if it's not what's being sorted by.

And move options struct into its own module

See https://github.com/mozilla/rust/pull/14310

This meant writing some libc interaction, which wasn't actually too bad.

Replace ~strs with either &'static strs or .to_owned() strs where appropriate
Fields now seem to be private by default - good!

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.