Now there are no more unwrap()s!

You can now have different columns per directory. So now, the Git column only appears when there's a Git repository in the current directory.

- Rename std::io to std::old_io

This is good for two reasons: 1) shorter code! 2) it won't fail if any of the filenames aren't valid UTF-8.

This is something that I've long wanted to add. It uses libgit2 as an optional dependency.

Extensions aren't ever displayed in lowercase, just compared case-insensitively, so this makes sense.

The widths come pre-computed, so there's no reason to keep them around in this table anymore.

Instead of stripping the ANSI formatting characters from our strings, work out the length without them and use that. This is per-column, but most of them are simple (just the same number of characters in the non-coloured string).

Sometimes, this is really simple: for example, trwxrwxrwx permissions strings are always going to be ten characters long, and the strings that get returned are chock full of ANSI escape codes.

This should have a small benefit on performance.