(lib.tex): Added entry for formatter module.

Doc/lib.tex

@@ -141,6 +141,7 @@ to Python and how to embed it in other applications.
 \input{liburlparse}
 \input{libhtmllib}
 \input{libsgmllib}
+\input{libformatter}
 \input{librfc822}
 \input{libmimetools}
 \input{libbinascii}