Add stream comand

This command allow the user to send the script to the STDIN
Sample of use:
```bash
$ melody stream < cat test.php
$ cat test.php | melody stream
$ curl http://my.private/snippets/demo.php | melody
```

The command is also the default one to let the user simply run
```bash
$ cat test.php | melody
$ curl http://my.private/snippets/demo.php | melody
```