Make live-preview hook and kill-buffer-hooks buffer-local

Take global hooks and make them buffer-local.
markdown-live-preview-remove-on-kill applies to both the Markdown buffers and
the buffers used to preview the export, so it needs to be re-added in two
places, where the export-viewing buffer is created, and when markdown-mode is
turned on.

The test test-markdown-ext/live-preview-exports adequately covers whether
these hooks run.

[jrblevin@sdf.org: Squashed two commits and rebased.
Added GH-63 PR text to commit message for reference.]

Signed-off-by: Jason Blevins <jrblevin@sdf.org>

markdown-mode.el

@@ -5313,7 +5313,9 @@ the rendered output."
       (let ((output-buffer
              (funcall markdown-live-preview-window-function export-file)))
         (with-current-buffer output-buffer
-          (setq markdown-live-preview-source-buffer cur-buf))
+          (setq markdown-live-preview-source-buffer cur-buf)
+          (add-hook 'kill-buffer-hook
+                    #'markdown-live-preview-remove-on-kill t t))
         (with-current-buffer cur-buf
           (setq markdown-live-preview-buffer output-buffer))))
     (with-current-buffer cur-buf
@@ -5912,6 +5914,10 @@ before regenerating font-lock rules for extensions."
   (add-hook 'window-configuration-change-hook
             'markdown-fontify-buffer-wiki-links t t)
 
+  ;; add live preview export hook
+  (add-hook 'after-save-hook #'markdown-live-preview-if-markdown t t)
+  (add-hook 'kill-buffer-hook #'markdown-live-preview-remove-on-kill t t)
+
   ;; do the initial link fontification
   (markdown-fontify-buffer-wiki-links))
 
@@ -5958,9 +5964,6 @@ before regenerating font-lock rules for extensions."
       (markdown-display-buffer-other-window (markdown-live-preview-export))
     (markdown-live-preview-remove)))
 
-(add-hook 'after-save-hook #'markdown-live-preview-if-markdown)
-(add-hook 'kill-buffer-hook #'markdown-live-preview-remove-on-kill)
-
 
 (provide 'markdown-mode)
 ;; Local Variables: