Add gravity flow demo

backend/wordpress/wp-content/plugins/wp-mail-smtp/wp-mail-smtp.php

@@ -0,0 +1,80 @@
+<?php
+
+if ( ! defined( 'ABSPATH' ) ) {
+	exit; // Exit if accessed directly.
+}
+
+/**
+ * Autoloader. Inspired by PSR-4 examples:
+ *
+ * @link https://github.com/php-fig/fig-standards/blob/master/accepted/PSR-4-autoloader-examples.md
+ *
+ * @since 1.0.0
+ *
+ * @param string $class The fully-qualified class name.
+ */
+spl_autoload_register( function ( $class ) {
+
+	list( $plugin_space ) = explode( '\\', $class );
+	if ( $plugin_space !== 'WPMailSMTP' ) {
+		return;
+	}
+
+	$plugin_folder = 'wp-mail-smtp';
+
+	// Default directory for all code is plugin's /src/.
+	$base_dir = WP_PLUGIN_DIR . '/' . $plugin_folder . '/src/';
+
+	// Get the relative class name.
+	$relative_class = substr( $class, strlen( $plugin_space ) + 1 );
+
+	/**
+	 * Normalize a filesystem path.
+	 * Copy of the `wp_normalize_path()` from WordPress 3.9.
+	 *
+	 * @since 1.2.0
+	 *
+	 * @param string $path
+	 *
+	 * @return string
+	 */
+	$normalize = function( $path ) {
+		$path = str_replace( '\\', '/', $path );
+		$path = preg_replace( '|(?<=.)/+|', '/', $path );
+		if ( ':' === substr( $path, 1, 1 ) ) {
+			$path = ucfirst( $path );
+		}
+		return $path;
+	};
+
+	// Prepare a path to a file.
+	$file = $normalize( $base_dir . $relative_class . '.php' );
+
+	// If the file exists, require it.
+	if ( is_readable( $file ) ) {
+		/** @noinspection PhpIncludeInspection */
+		require_once $file;
+	}
+} );
+
+/**
+ * Global function-holder. Works similar to a singleton's instance().
+ *
+ * @since 1.0.0
+ *
+ * @return WPMailSMTP\Core
+ */
+function wp_mail_smtp() {
+	/**
+	 * @var \WPMailSMTP\Core
+	 */
+	static $core;
+
+	if ( ! isset( $core ) ) {
+		$core = new \WPMailSMTP\Core();
+	}
+
+	return $core;
+}
+
+wp_mail_smtp();