Foam: Update for new API, always circular; new SFX

Never change aspect ratio of bubble image used by Foam.
New sound effect, CC-0 by https://freesound.org/people/ristooooo1

docs/CHANGES.txt

@@ -40,6 +40,7 @@ https://tuxpaint.org/
       + Bricks
       + Clone
       + Confetti
+      + Foam
       + Googly Eyes
       + Light
       + Metal Paint
@@ -60,6 +61,13 @@ https://tuxpaint.org/
     * Clone performance improved.
       Bill Kendrick <bill@newbreedsoftware.com>
 
+    * Foam bubbles now always appear circular.
+      Bill Kendrick <bill@newbreedsoftware.com>
+
+    * New Foam sound effect.
+      (Sound effect licensed as Creative Commons 0 by
+      https://freesound.org/people/ristooooo1)
+
   * Other Improvements:
     -------------------
     * Word-wrap long button labels, for better readability.