Add stream comand

This command allow the user to send the script to the STDIN
Sample of use:
```bash
$ melody run < test.php
$ cat test.php | melody run
$ curl https://gist.githubusercontent.com/lyrixx/565752f13499a3fa17d9/raw/f561159b09a2014dd0d75727582c2cf8ee36e30e/melody.php | melody run
```

By side effect, it allow every stream supported by php to the `run` command
* http => `melody run http://my-server/script.php`
* ftp => (not tested)
* ...

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
```

GistHandler allow Gist URI (like https://gist.github.com/lyrixx/565752f13499a3fa17d9).
If StreamHandler was before the GistHandler, it will download the html Gist's page and try to run it.

BTW, the method `GistHandler::supports` just run a RegExp to check the input. It should be realy quick.