Introduce custom PSR-4 autoload if not using composer

autoload.php

@@ -0,0 +1,35 @@
+<?php
+
+/**
+ * Based on https://www.php-fig.org/psr/psr-4/examples/
+ */
+spl_autoload_register(function ($class) {
+
+    // project-specific namespace prefix
+    $prefix = 'Algolia\\AlgoliaSearch\\';
+
+    // base directory for the namespace prefix
+    $base_dir = __DIR__ . '/src/';
+
+    // does the class use the namespace prefix?
+    $len = strlen($prefix);
+    if (strncmp($prefix, $class, $len) !== 0) {
+        // no, move to the next registered autoloader
+        return;
+    }
+
+    // get the relative class name
+    $relative_class = substr($class, $len);
+
+    // replace the namespace prefix with the base directory, replace namespace
+    // separators with directory separators in the relative class name, append
+    // with .php
+    $file = $base_dir . str_replace('\\', '/', $relative_class) . '.php';
+
+    dump($file);
+
+    // if the file exists, require it
+    if (file_exists($file)) {
+        require $file;
+    }
+});