use nil for empty lists
improve doc-strings
enforce use of spaces for indentation
split into sections and rearrange

* slit into sections
* move variables to where they are used
* move -build-exec-point-alist to "Draw Buffer"
* move -get-key-map to "Storing Keymaps"
* move boring commands to end of file
  (help, mouse-exec, next-exec, kill-buffer)
remove magit-key-mode-de-generate
save wip