Plugin structure (#25)

* Plugin structure
* added unit tests to cover constructors

Author: athlan

includes/class-customfieldspermalink.php

@@ -0,0 +1,39 @@
+<?php
+/**
+ * Class Updater
+ *
+ * @package WordPress_Custom_Fields_Permalink
+ */
+
+namespace CustomFieldsPermalink;
+
+/**
+ * Class Plugin_Updater handles the upgrade process.
+ */
+class Plugin_Updater {
+
+	/**
+	 * This hook is called once any activated plugins have been loaded.
+	 *
+	 * @link https://codex.wordpress.org/Plugin_API/Action_Reference/plugins_loaded
+	 */
+	public function on_init_hook() {
+		$version_option_name = '_wordpress_custom_fields_permalink_plugin_version';
+		$version_from        = get_option( $version_option_name, null );
+		$version_to          = WORDPRESS_CUSTOM_FIELDS_PERMALINK_PLUGIN_VERSION;
+		if ( $version_from != $version_to ) {
+			$this->update_plugin( $version_from, $version_to );
+			update_option( $version_option_name, $version_to, true );
+		}
+	}
+
+	/**
+	 * Upgrades the plugin.
+	 *
+	 * @param string $version_from Currently running version.
+	 * @param string $version_to   Version upgrade to.
+	 */
+	private function update_plugin( $version_from, $version_to ) {
+		flush_rewrite_rules();
+	}
+}