Implement %AutoFormat.RemoveEmpty, end to start ref, and injector rewind.

Injector rewind: Injectors can now use the method rewind() in order to move
the input index backwards, so that they can reprocess tokens (other injectors
are not affected by a rewind). This functionality was necessary to implement
nested node removals in %AutoFormat.RemoveEmpty.

End to start ref: To facilitate rewinding, HTMLPurifier_Token_End now
maintains a reference called $start to the starting token for their node.

%AutoFormat.RemoveEmpty removes empty nodes. Lots of people have requested
it, so here is a partially effective implementation. Because it is implemented
as an Injector, it's not possible for it to handle newly introduced empty
nodes by later validators, specifically auto-closing and child validation.
The Injector is only meant to be used on HTML-ish languages.

Signed-off-by: Edward Z. Yang <edwardzyang@thewritingpot.com>

NEWS

@@ -18,8 +18,12 @@ NEWS ( CHANGELOG and HISTORY )                                     HTMLPurifier
 ! Proper support for name attribute. It is now allowed and equivalent to the id
   attribute in a and img tags, and is only converted to id when %HTML.TidyLevel 
   is heavy (for all doctypes).
+! %AutoFormat.RemoveEmpty to remove some empty tags from documents. Please don't
+  use on hand-written HTML.
 . Strategy_MakeWellFormed now operates in-place, saving memory and allowing
   for more interesting filter-backtracking
+. New HTMLPurifier_Injector->rewind() functionality, allows injectors to rewind
+  index to reprocess tokens.
 
 3.1.1, released 2008-06-19
 # %URI.Munge now, by default, does not munge resources (for example, <img src="">)