Add sntp-time-sync example

examples/sntp-time-sync/Makefile

@@ -0,0 +1,10 @@
+PROG ?= example
+
+all: $(PROG)
+	$(RUN) ./$(PROG) $(ARGS)
+
+$(PROG): main.c
+	$(CC) ../../mongoose.c -I../.. -W -Wall -DMG_ENABLE_LINES=1 $(CFLAGS) -o $(PROG) main.c
+
+clean:
+	rm -rf $(PROG) *.o *.dSYM *.gcov *.gcno *.gcda *.obj *.exe *.ilk *.pdb