stats command

Corresponding to "Nodes Stats API"

```
http://www.elasticsearch.org/guide/reference/api/admin-cluster-nodes-stats.html
```

... or "Index Status API"

```
http://www.elasticsearch.org/guide/reference/api/admin-indices-stats.html
```

Make the default output some easily readable format, but also with option like `--output-graphite` or `--output-statsd` to print the stats in popular formats for graphing would be nice to have.

Start by reading the referenced Nodes Stats API and Index Status API documentation, then inspect the repository's existing command entry points to determine where a stats command belongs. Define the readable default output and the requested Graphite or StatsD formats before implementation; done means the command retrieves the selected Elasticsearch stats and emits each supported format.

Written by the indexing model from the issue text.