Added [Alt]+[S] key sequence to mute/unmute sound effects.

(Does not override "--nosound" option!)

docs/html/OPTIONS.html

@@ -23,7 +23,7 @@ New Breed Software</p>
 <p><a href="mailto:bill@newbreedsoftware.com">bill@newbreedsoftware.com</a><br>
 <a href="http://www.newbreedsoftware.com/tuxpaint/">http://www.newbreedsoftware.com/tuxpaint/</a></p>
 
-<p>October 2, 2005</p>
+<p>November 12, 2005</p>
 </center>
 
 <hr size=2 noshade>
@@ -119,7 +119,8 @@ New Breed Software</p>
 
   <dt><code><b>nosound=yes</b></code></dt>
   <dd>
-    Disable sound effects.
+    Disable sound effects.  (Note: Pressing <b>[Alt]</b>&nbsp;+&nbsp;<b>[S]</b>
+    cannot be used to reenable sounds if they were disabled using this option.)
   </dd>
 
   <dt><code><b>noquit=yes</b></code></dt>