[svn-r1678] Tools.html

Palettes.html
	Various copy-edits and cleaned up HTML.
Caching.html
	Edited section headers and added an <h1> header.
Errors.html
	Added section title "Error Handling Operations."

doc/html/Errors.html

@@ -62,6 +62,8 @@
       next API function which is called (with a few exceptions) resets
       the stack.
 
+    <h2>2. Error Handling Operations</h2>
+
     <p>In normal circumstances, an error causes the stack to be
       printed on the standard error stream.  The first item, number
       "#000" is produced by the API function itself and is usually