This autoloader will search for Foo\Bar\Baz (for example) in ./Foo/Bar/Baz.php, ./Foo/Bar.php and ./Foo.php, in that order. This enables developers to place multiple classes and even multiple namespaces in one file when appropriate. Just place this file in your src/ directory and use it as the entry point for your project.

simple-autoload.php

<?php

spl_autoload_register(function ($cls) {
    for ($cls = explode('\\', $cls); $cls; array_pop($cls)) {
        $sep = DIRECTORY_SEPARATOR;
        $php = __DIR__ . $sep . join($sep, $cls) . '.php';
        if (file_exists($php)) {
            /** @noinspection PhpIncludeInspection */
            require_once $php;
            break;
        }
    }
});