Logging

We need to add some logging to the `Client` class. For each request the client makes, we should output a detailed debug message to a logger of some sort. I really like how Tire does it; logging a curl command that you can copy/paste and use directly. Also, outputting the status code of the response would be good, too ...

```
[200] curl -XGET 'http://localhost:9200/index/_search' -d '...'
```

Not sure how to handle large bodies and what not. And I don't think we need to log responses.

cc @github/search

Start by locating the Client class and tracing how it makes requests and receives responses. Review the project's existing logger conventions, then determine how to represent the request as a copyable curl command, handle large bodies, and include the response status without logging responses. Done means each request produces the agreed debug output with suitable tests.

索引モデルが issue の本文から書いたものです。