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/Doc/lib/libsets.tex b/Doc/lib/libsets.tex
index 5f199a0..8ce62c8 100644
--- a/Doc/lib/libsets.tex
+++ b/Doc/lib/libsets.tex
@@ -100,9 +100,8 @@
 \end{tableii}
 
 In addition to the above operations, both \class{Set} and \class{ImmutableSet}
-support set to set comparison operators based on the contents of their
-internal dictionaries.  Two sets are equal if and only if every element of
-each set is contained in the other.
+support set to set equality comparisons.  Two sets are equal if and only if
+every element of each set is contained in the other.
 
 The following table lists operations available in \class{ImmutableSet}
 but not found in \class{Set}: