feat(daemon) `ipfs daemon --initialized`

With this PR, users can fetch and run ipfs in _one_ command.

```
docker run -d -p 4001:4001 -p 5001:5001 jbenet/go-ipfs daemon --initialized
```

Magic.

nb: needs https://github.com/jbenet/go-datastore/pull/9
>  importing our `errors` package as errors is okay since the only thing exported by Go's package is `errors.New`

Okay, since ours also provides `New`.

Ah, so our own `Errorf` adds functionality, okay, fine by me. thanks for addressing!