Adding possibility to set custom search handler on creating SOLR client.

Add possibility to set custom search handler on creating solr client.
Now you ca set an custom handler without using "qt" parameter.

```js
function createClient(host, port, core, path, handler){
  var options = (typeof host === 'object')? host : {
      host : host,
      port : port,
      core : core,
      path : path,
      handler : handler
   };
  return new Client(options);
}
```