modified:   linked_list.c
        Solve a memory leak on the function : insert_at_linked_list.
	modified:   main.c
        Add many options :
            -h for help.
            -s [N] for printing the speed of the insertion, lookup and deletion over a list of N elements.
            -r [E1, E2, ..., EN] to try the different function implementations over the initial list [E1, E2, ..., EN].
        Now the user do not type the list after running the program but by passing arguments.