Add keybinding to jump to top/bottom of listing.

Uses single g for top (as in less) and G for bottom.

This provides a more extensible way to check entry type. Now it's easier to add color definitions to other types (see stat(2)).

Previously we're using lstat() to make file sizes reflect the actual size occupied by an entry (symbolic links are just small references). However, we need to dereference links in order to know the correct type of their target.

Quick and dirty support for cd in bash and zsh