Fix html5lib#72: rewrite the sanitizer to be a treewalker filter only.

As we no longer need the sanitizer to be shared between a filter and
a tokenizer, move the entire sanitizer to the filter module.

Author: gsnedders

CHANGES.rst

@@ -40,6 +40,10 @@ Released on XXX
   and the new default), and "spec" (the old False value, and the old
   default).**
 
+* **Fix #72 by rewriting the sanitizer to apply only to treewalkers
+  (instead of the tokenizer); as such, this will require amending all
+  callers of it to use it via the treewalker API.**
+
 
 0.9999999/1.0b8
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