Class autoloader added

src/Steein/SDK/autoload.php

@@ -0,0 +1,58 @@
+<?php
+/**
+ * You only need this file if you are not using composer.
+ * Why are you not using composer?
+ * https://getcomposer.org/
+ */
+
+if (version_compare(PHP_VERSION, '5.5.0', '<')) {
+    throw new Exception('The Steein SDK requires PHP version 5.5 or higher.');
+}
+
+require_once __DIR__ . '/functions.php';
+
+/**
+ * Register the autoloader for the Steein SDK classes.
+ *
+ * Based off the official PSR-4 autoloader example found here:
+ * https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-4-autoloader-examples.md
+ *
+ * @param string $class The fully-qualified class name.
+ *
+ * @return void
+ */
+spl_autoload_register(function ($class) {
+    // project-specific namespace prefix
+    $prefix = 'Steein\\SDK\\';
+
+    // For backwards compatibility
+    $customBaseDir = '';
+    // @todo v6: Remove support for 'Steein_SDK_V4_SRC_DIR'
+    if (defined('Steein_SDK_V4_SRC_DIR')) {
+        $customBaseDir = Steein_SDK_V4_SRC_DIR;
+    } elseif (defined('Steein_SDK_SRC_DIR')) {
+        $customBaseDir = Steein_SDK_SRC_DIR;
+    }
+    // base directory for the namespace prefix
+    $baseDir = $customBaseDir ?: __DIR__ . '/';
+
+    // 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
+    $relativeClass = substr($class, $len);
+
+    // replace the namespace prefix with the base directory, replace namespace
+    // separators with directory separators in the relative class name, append
+    // with .php
+    $file = rtrim($baseDir, '/') . '/' . str_replace('\\', '/', $relativeClass) . '.php';
+
+    // if the file exists, require it
+    if (file_exists($file)) {
+        require $file;
+    }
+});