Clean generated *.su file and gitignore them
diff --git a/library/Makefile b/library/Makefile
index 45ed148..50faed9 100644
--- a/library/Makefile
+++ b/library/Makefile
@@ -200,7 +200,7 @@
 
 clean:
 ifndef WINDOWS
-	rm -f *.o libmbed*
+	rm -f *.o *.su libmbed*
 else
-	del /Q /F *.o libmbed*
+	del /Q /F *.o *.su libmbed*
 endif