Configurable host and port

Added configuration options to specify host and port for ElasticSearch

```
  var elasticsearch = require('elasticsearch')({
    index : 'kitteh',
    host : 'ohai.kthxbai.com',
    port : 9200
  });

  elasticsearch.query({query: {field: {field1: 'hai'}}}, function(err, results) {
    console.log(results);
  });
```