Fix #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 +40,8 @@ Released on XXX
   and the new default), and "spec" (the old False value, and the old
   default).**
 
+* Sanitizer change XXX
+
 
 0.9999999/1.0b8
 ~~~~~~~~~~~~~~~