Added entries for difflib documentation.

Doc/Makefile.deps

@@ -54,6 +54,7 @@ LIBFILES= $(MANSTYLES) $(COMMONTEX) \
 	../lib/libfpectl.tex \
 	../lib/libgc.tex \
 	../lib/libweakref.tex \
+	../lib/libdifflib.tex \
 	../lib/libdoctest.tex \
 	../lib/libtypes.tex \
 	../lib/libtraceback.tex \

Doc/lib/lib.tex

@@ -103,6 +103,7 @@ and how to embed it in other applications.
 \input{libstring}
 \input{libre}
 \input{libstruct}
+\input{libdifflib}
 \input{libfpformat}
 \input{libstringio}
 \input{libcodecs}