Fixed #465. Add option for including script source files.

Readme.org

@@ -803,15 +803,22 @@ This feature is turned off by default and needs to be switched on with ~org-reve
    .html file. Provide your audience with a link to the client file to allow
    them to track your presentation on their own device.
 
-** Extra Stylesheets
+** Extra Stylesheets and Script Sources
 
-   Set =REVEAL_EXTRA_CSS= to a stylesheet file path in order to load extra custom
+   Set =REVEAL_EXTRA_CSS= to a stylesheet file path to load extra custom
    styles after loading a theme.
 
+   Set =REVEAL_EXTRA_SCRIPT_SRC` to script file path to load extra
+   script sources.
+
 #+BEGIN_SRC org
-,#+REVEAL_EXTRA_CSS: url-to-custom-stylesheet.css
+  ,#+REVEAL_EXTRA_CSS: url-to-custom-stylesheet.css
+  ,#+REVEAL_EXTRA_SCRIPT_SRC: url-to-custom-script
 #+END_SRC
 
+   Same setup can be done globally by customize variables
+ ~org-reveal-extra-css~ and ~org-reveal-extra-script-src~.
+
 ** Select Built-In Scripts
 
    Set option =REVEAL_PLUGINS= or variable =org-reveal-plugins= to a

ox-reveal.el

@@ -100,6 +100,7 @@
     (:reveal-default-frag-style "REVEAL_DEFAULT_FRAG_STYLE" nil org-reveal-default-frag-style t)
     (:reveal-single-file nil "reveal_single_file" org-reveal-single-file t)
     (:reveal-extra-script "REVEAL_EXTRA_SCRIPT" nil org-reveal-extra-script space)
+    (:reveal-extra-script-src "REVEAL_EXTRA_SCRIPT_SRC" nil org-reveal-extra-script-src split)
     (:reveal-init-options "REVEAL_INIT_OPTIONS" nil org-reveal-init-options newline)
     (:reveal-highlight-css "REVEAL_HIGHLIGHT_CSS" nil org-reveal-highlight-css nil)
     (:reveal-reveal-js-version "REVEAL_REVEAL_JS_VERSION" nil nil t)
@@ -319,6 +320,11 @@ Example:
   :group 'org-export-reveal
   :type 'string)
 
+(defcustom org-reveal-extra-script-src '()
+  "Custom script source that will be embedded in a <script src> tag."
+  :group 'org-export-reveal
+  :type 'list)
+
 (defcustom org-reveal-highlight-css "%r/lib/css/zenburn.css"
   "Highlight.js CSS file."
   :group 'org-export-reveal
@@ -813,7 +819,12 @@ Reveal.initialize({
                           ",\n")
                ;; Extra initialization scripts
                (or (plist-get info :reveal-extra-script) "")))
-)))
+     ;; Extra <script src="..."></script> tags
+     (let ((src-list (plist-get info :reveal-extra-script-src)))
+       (and src-list
+            (mapconcat (lambda (src) (format "<script src=\"%s\"></script>" src))
+                       src-list
+                       "\n"))))))
 
 (defun org-reveal--read-sexps-from-string (s)
   (let ((s (string-trim s)))