Implements Config and Logging plugins, tidies Main

Added Database and Flatfile plugin engines for both Config and Log classes.
Rewrote Main to make use of the new plugins.
Updated config file definitions to make use of plugins.

source/lib/Sihnon/Main.class.php

@@ -1,26 +1,37 @@
 <?php
 
 class Sihnon_Main {
-
-    private static $instance;
-
-    private $config;
-    private $database;
-    private $log;
-    private $cache;
     
-    private $base_uri;
+    protected static $instance;
 
-    private function __construct() {
-        $this->config   = new Sihnon_Config(Sihnon_DBConfig);
-        $this->database = new Sihnon_Database($this->config);
-        $this->config->setDatabase($this->database);
+    protected $config;
+    protected $database;
+    protected $log;
+    protected $cache;
+    
+    protected $base_uri;
 
-        $this->log      = new Sihnon_Log($this->database, $this->config, Sihnon_Log_Table);
-        $this->cache    = new Sihnon_Cache($this->config);
-        
+    protected function __construct() {
         $this->base_uri = dirname($_SERVER['SCRIPT_NAME']) . '/';
     }
+    
+    protected function init() {
+        if (Sihnon_DatabaseSupport) {
+            $this->database = new Sihnon_Database(Sihnon_DBConfig);
+        }
+
+        $this->config = new Sihnon_Config(Sihnon_ConfigPlugin, array(
+        	'database' => $this->database,
+        	'table' => Sihnon_ConfigTable, 
+        	'filename' => Sihnon_ConfigFile)
+        );
+        
+        $this->log    = new Sihnon_Log($this->config->get('logging.plugin'), array(
+        	'database' => $this->database)
+        );
+                
+        $this->cache  = new Sihnon_Cache($this->config);
+    }
 
     /**
      * 
@@ -29,6 +40,7 @@ class Sihnon_Main {
     public static function instance() {
         if (!self::$instance) {
             self::$instance = new Sihnon_Main();
+            self::$instance->init();
         }
 
         return self::$instance;
@@ -111,6 +123,18 @@ class Sihnon_Main {
         }
     }
     
+    /**
+     * Throws an exception if the requested name has not been defined.
+     * 
+     * @param string $name Name of the definition to check for the existence of
+     * @throws Sihnon_Exception_MissingDefinition
+     */
+    public static function ensureDefined($name) {
+        if (! defined($name)) {
+            throw new Sihnon_Exception_MissingDefinition($name);
+        }
+    }
+    
     public static function mkdir_recursive($directory, $permissions=0777) {
         $parts = explode('/', $directory);
         $path = '';