Don't auto fill metadata lines in Nikola reST files.

nikola-metadata-nobreak.el

;; Nikola metadata lines start like this:
;; .. keyword:
;; They shouldn't be wrapped.
(defvar tkb-nikola-metadata-regexp "\\.\\. [a-z]+:")

(defun tkb-nikola-rest-fill-nobreak-p ()
  "Don't fill on metadata lines in nikola reST posts."
  (save-excursion
    (beginning-of-line)
    (looking-at tkb-nikola-metadata-regexp)))

(defun tkb-nikola-rest-hook ()
  (interactive)
  (when (and (string-match "\\.rst\\'" (buffer-file-name))
             (looking-at tkb-nikola-metadata-regexp))
    (make-local-variable 'fill-nobreak-predicate)
    (setq fill-nobreak-predicate (list #'tkb-nikola-rest-fill-nobreak-p))))

(add-to-list 'find-file-hook #'tkb-nikola-rest-hook)