[Feature] Multiple namespaces to look for endpoints

[zoliszabo]

Adds possibility to define multiple locations (namespaces) where WpClient can look after endpoints.
This feature is useful where custom, domain-specific endpoints are used.

How to use:

Your new endpoint (notice the namespace):

namespace Your\Special\Endpoint;

use Vnn\WpApiClient\Endpoint\AbstractWpEndpoint; 

class Examples extends AbstractWpEndpoint
{
...
}

And where it is added to WpClient:

$client = new WpClient(...);
$client->addEndpointNamespace('Your\Special\Endpoint\\');
$client->examples()->get(1);

[pekka]

This PR was a huge help for me today - thank you!

[zoliszabo]

This PR was a huge help for me today - thank you!

You're welcome! :)

[zack-carlson]

#29 (comment)