add cli for writing

e.g.

```
$ cat ~/Downloads/Pelican\ -\ Forever\ Becoming\ \(2013\)/01.\ Terminal.mp3 | cabs test
{ start: 0,
  end: 5242880,
  hash: 'cljbrq0xepacaadz52cfb76jkeaoxi5196refogfad5hvejh5xuyv4eqli2r2w9615fj22jrtqe' }
{ start: 5242880,
  end: 8858199,
  hash: 'bef8zn0fxghdwx6x714njeule4m8midpxd8cprllva9rtqbbywcuu7jmsycty9b9x6bhs0jeuqw' }
```