Support class name references (aliases) in Container configuration

[clue]

This changeset adds support for class name references (aliases) in the Container configuration. This allows us to fine-tune the autowiring behavior and explicitly overwrite autowiring defaults for more advanced use cases. This does not otherwise break existing APIs, so this is a pure feature addition.

<?php

use FrameworkX\Container;
use Psr\Http\Message\ResponseInterface;
use React\Cache\ArrayCache;
use React\Cache\CacheInterface;
use React\Http\Message\Response;

// …

$container = new Container([
    ResponseInterface::class => Response::class,
    CacheInterface::class => function () {
        return ArrayCache::class;
    }
]);

// …

Builds on top of #95