Support PSR-11 container interface by using DI container as adapter

[clue]

This changeset adds support for the PSR-11 container interface by using the DI container as an adapter. This allows using custom DI containers with X for more advanced use cases. This does not otherwise break existing APIs, so this is a pure feature addition.

<?php

require __DIR__ . '/../vendor/autoload.php';

// $builder = new DI\ContainerBuilder();
// $builder->...
// $container = $builder->build();
$container = new DI\Container();

$app = new FrameworkX\App(new FrameworkX\Container($container));

$app->get('/', Acme\Todo\HelloController::class);
$app->get('/users/{name}', Acme\Todo\UserController::class);

$app->run();

Builds on top of #95
Closes #159
Refs #30