modified:   main.c
        Modify the program to use the arguments.
        Add arguments :
            -h, --help to print help.
            -t, --test [E1, E2, ..., EN] to test the stack with the elements [E1, E2, ..., EN].
            -s, --speed [N] to compute [N] insertions and [N] deletions and print the speed for each steps.
	modified:   stack.c
            Add function "print_stack" to print the stack.
            Add function "top_stack" to get the element  the top of the stack.
	modified:   stack.h
            Add functions prototype "print_stack" and "top_stack".