editor modes:

    - NORMAL: select and manipulate text

    - INSERT: add and remove text

    - COMMAND: execute built in commands

    - RUN: execute external commands

    - EDIT: apply structural regular expressions


    - unlike vi, ad's motions in NORMAL mode are "noun verb" as in kakoune
      rather than "verb noun" model you might expect

        - the NORMAL mode keymap is located here: ../../src/mode/normal.rs

