Support DSN configuration style for Elastica client

[Tristan971]

In Elastically's client's constructor, initialisation of the factory is triggered in the following line:

elastically/src/Client.php

Lines 37 to 38 in 06218e5

	// BC Layer, to remove in 2.0
	$this->factory = new Factory($config);

This causes Elastically to require an array-style configuration for Elastica, even Elastica supports DSN-style configuration. This causes an issue when trying to use a DSN:

In Factory.php line 53:
                                                                                                                                            
  JoliCode\Elastically\Factory::__construct(): Argument #1 ($config) must be of type array, string given, called in .../vendor/jolicode/elastically/src/Client.php on line 38                                                                                
                                                                                                                                            

It would probably look nicer in general to have the Elastica client instance split away from the Elastically one

[lyrixx]

I like it. Would you mind to submit a PR?

[Tristan971]

I can sketch something out in the next few days and see if it looks good