Added acky.s3

All methods tested.
I'm not clear what can be passed in.

```
get() # list the contents of all buckets?
get("blarg") # list contents of bucket "blarg"?
get("blarg/foo") # list contents of directory "foo" in bucket "blarg"?
get("/") # ???
```

I think it's fair to say "path is an s3 url. Omitting path or providing the root URL (s3://) will return a list of all buckets"