Removed < <= > >= from the API.  Implemented as comparisons of the
underlying dictionaries, there were no reasonable use cases (lexicographic
sorting of a list of sets is somewhat esoteric).  Frees the operators
for other uses (such as strict subset and superset comparisons).

Updated documentation and test suite accordingly.
diff --git a/Lib/test/test_sets.py b/Lib/test/test_sets.py
index 9ff98a6..65b48e2 100644
--- a/Lib/test/test_sets.py
+++ b/Lib/test/test_sets.py
@@ -419,12 +419,12 @@
 
     def test_cmp(self):
         try:
-            self.other < self.set
+            self.other == self.set
             assert 0, "Comparison with non-set on left"
         except TypeError:
             pass
         try:
-            self.set >= self.other
+            self.set != self.other
             assert 0, "Comparison with non-set on right"
         except TypeError:
             pass