Added entries for difflib documentation.
diff --git a/Doc/lib/lib.tex b/Doc/lib/lib.tex
index 58e011f..5dde036 100644
--- a/Doc/lib/lib.tex
+++ b/Doc/lib/lib.tex
@@ -103,6 +103,7 @@
 \input{libstring}
 \input{libre}
 \input{libstruct}
+\input{libdifflib}
 \input{libfpformat}
 \input{libstringio}
 \input{libcodecs}