manual: Add Graphviz.

manual.scrbl

@@ -3,7 +3,8 @@
 @(require (for-label (only-in typed/racket
 	  	      require/typed require/typed/provide
 		      Any Boolean Void Sequenceof Listof List U False Number Values
-		      Natural HashTable Mutable-HashTable Immutable-HashTable))
+		      Natural HashTable Mutable-HashTable Immutable-HashTable
+		      Output-Port))
   	  (for-label (only-in math/matrix Matrix))
 	  (for-label (only-in graph (matrix-graph? g:matrix-graph?)))
 	  (for-label (only-in data/gen-queue/fifo mk-empty-fifo))
@@ -202,6 +203,13 @@ Graph properties are not supported.
 @defproc[(bipartite? [g Graph]) (U (List (Listof Any) (Listof Any)) False)]{}
 @defproc[(maximum-bipartite-matching [g Graph]) (Listof (List Any Any))]
 
+@subsection{Graphviz}
+
+@defproc[(graphviz [g Graph]
+		   [#:output output Output-Port #f]
+		   [#:colors colors (HashTable Any Natural) #f])
+		   String]{}
+
 @section{License}
 
 Like the generic graph library, this library is licensed under the Apache