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
Fallback to `TAB' if `<tab>' is not bound

Since `<tab>' is translated to `TAB' by default, when falling back to the original binding, ensure that you fall back to `TAB' in cases where `<tab>' has not been bound by user.  Fixes #16
Merge pull request #17 from jleechpe/patch-1

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