first commit
darkroom-mode added
Now works with multiple windows for same darkroom buffer

* darkroom.el (darkroom-set-margins): set for every window separately.
(darkroom-fill-paragraph-maybe): Be smarter we filling
paragraph. TODO: use remap.
(darkroom-saved-mode-line-format)
(darkroom-saved-header-line-format)
(darkroom-saved-visual-line-mode): new buffer-local vars.
(darkroom-visual-mode-maybe-enable): new function.
(darkroom-mode): Remove hack here.
(darkroom-maybe-enable): new function.
(darkroom-tentative-mode): New minor mode.
Leave darkroom-mode when leaving tentative-mode

* darkroom.el (darkroom-tentative-mode): Leave minor mode as well when leaving
tentative-mode.