Replace `map` with `outline-minor-mode-map` when defining keys

Let binding is not needed when replacing all instances of `map` with `outline-minor-mode-map`.  Indentation adjusted for line length.  Fixes `Could not deduce mode name from keymap name` error [ #16 ]

Second commit adds test to fall back to `TAB` if `<tab>` has not been manually bound by user.  If `<tab>` is bound, use it.

Testing this way is more efficient than mapping to `TAB` directly, since `TAB` also influences <kbd>C-i</kbd>.