ox-html: Add webp as an inline image format

* lisp/ox-html.el (org-html-inline-image-rules): Add webp as an inline
  image format

Webp is an image format introduced in 2010, which now has widespread
support in browsers. ox-html can inline webp images identically to how
it does already for other image formats.

[km: updated package-version keyword and added NEWS entry]

Signed-off-by: Jay Kamat <jaygkamat@gmail.com>

etc/ORG-NEWS

@@ -101,6 +101,10 @@ that asks whether to clock out and save when there's a running clock.
 Customize ~org-clock-ask-before-exiting~~ to nil to disable this new
 behavior.
 
+*** Option ~org-html-inline-image-rules~ now includes .webp
+
+By default ox-html now inlines webp images.
+
 ** New features
 *** =ob-python= improvements to =:return= header argument 
 

lisp/ox-html.el

@@ -848,16 +848,15 @@ link to the image."
   :type 'boolean)
 
 (defcustom org-html-inline-image-rules
-  `(("file" . ,(regexp-opt '(".jpeg" ".jpg" ".png" ".gif" ".svg")))
-    ("http" . ,(regexp-opt '(".jpeg" ".jpg" ".png" ".gif" ".svg")))
-    ("https" . ,(regexp-opt '(".jpeg" ".jpg" ".png" ".gif" ".svg"))))
+  `(("file" . ,(regexp-opt '(".jpeg" ".jpg" ".png" ".gif" ".svg" ".webp")))
+    ("http" . ,(regexp-opt '(".jpeg" ".jpg" ".png" ".gif" ".svg" ".webp")))
+    ("https" . ,(regexp-opt '(".jpeg" ".jpg" ".png" ".gif" ".svg" ".webp"))))
   "Rules characterizing image files that can be inlined into HTML.
 A rule consists in an association whose key is the type of link
 to consider, and value is a regexp that will be matched against
 link's path."
   :group 'org-export-html
-  :version "24.4"
-  :package-version '(Org . "8.0")
+  :package-version '(Org . "9.5")
   :type '(alist :key-type (string :tag "Type")
 		:value-type (regexp :tag "Path")))