added debug handler: ElasticSearch\Client::addOnCallHandler

[juzna]

It is possible to register a callback, which gets called every time a request to ElasticSearch is made.

It makes possible to create debug tools, such as this debug bar for Nette Fw.

[nervetattoo]

Thanks. I'd appreciate a few small changes before merging:

1. Change the public $onCall to a protected $onCall = array(). I don't want this exposed
2. Preferably add typehinting in the method for adding a listener
3. I would prefer a method name like onCall
4. Add some basic tests to prove its working

[juzna]

Hi Raymond, thanks for the feedback! I don't understand what you mean by the third step, can you please give me a better hint? Thx

[nervetattoo]

Just that I think a method named onCall(callable $handler) would be better than addOnCallHandler($handler)