Add stream comand

This command allow the user to send the script to the STDIN
Sample of use:
```bash
$ melody stream < test.php
$ cat test.php | melody stream
$ curl https://gist.githubusercontent.com/lyrixx/565752f13499a3fa17d9/raw/f561159b09a2014dd0d75727582c2cf8ee36e30e/melody.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
```

is_readable expects a exting file. StreamHandler should run on every resources (http://, php://, etc...)