datastore: _action_All methods removed.

(RE: #41)

`saveAll` -> `save`
`delAll` -> `delete`
`getAll` -> `get`

For `save`, it accepts either a single object, or an array of objects formatted like:

```js
{
  key: ['Kind', null],
  data: {
    arbitrary: 'value'
  }
}
```
I think `callback && callback(err);` is legacy. We can do `this.makeReq('commit', req, callback);` here.