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/Exceptions.class.php

@@ -2,6 +2,9 @@
 
 class Sihnon_Exception extends Exception {};
 
+class Sihnon_Exception_NotImplemented         extends Sihnon_Exception {};
+class Sihnon_Exception_MissingDefinition      extends Sihnon_Exception {};
+
 class Sihnon_Exception_DatabaseException      extends Sihnon_Exception {};
 class Sihnon_Exception_DatabaseConfigMissing  extends Sihnon_Exception_DatabaseException {};
 class Sihnon_Exception_DatabaseConnectFailed  extends Sihnon_Exception_DatabaseException {};