- Handle things like "$-10"
- docs.rs documentation
- Implement printing only a screenful at a time (real ed doesn't bother to do this)
- Save preferences as distinct from saving state
  - Load from preferences in $XDG_CONFIG_HOME/edhex/preferences if they exist
    - If not provided, should be in $HOME/.config per the XDG Basedir specification
      https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
