streaming output

I was looking into a pull to support the yes command but it doesn't look like cash supports streaming of large output streams, one could simulate the yes command in node pretty easily with something like

``` js
function yes(explative) {
explative = explative || 'y';
return new stream.Readable({
read() {
var moreNeeded = true;
while (moreNeaded) {
this.push(explative);
moreNeeded = this.push(os.sep);
}
}
});
}
```

but as far as I could tell there is no way to output stuff continually async wise so that you could catch signals

The issue names no files or tests; start by tracing Cash's output handling and its use of Node streams. Determine how continuous asynchronous output should work while still allowing signal handling, then verify the behavior with a command that produces an ongoing stream.

Written by the indexing model from the issue text.