manual: Add All-pairs Shortest Paths.

manual.scrbl

@@ -180,6 +180,11 @@ Graph properties are not supported.
 			     (Values (Mutable-HashTable Any Number)
                                      (Mutable-HashTable Any Any))]{}
 
+@subsection{All-pairs Shortest Paths}
+@defproc[(floyd-warshall [g Graph]) (Mutable-HashTable (List Any Any) Number)]{}
+@defproc[(transitive-closure [g Graph]) (Mutable-HashTable (List Any Any) Boolean)]{}
+@defproc[(johnson [g Graph]) (Mutable-HashTable (List Any Any) Number)]{}
+
 @section{License}
 
 Like the generic graph library, this library is licensed under the Apache