changes in \Tizo\TIZO class:

 - remove ::$level_loading_relative_to() method
 - tizo level paths must be absolute!
 - check value of static::$config['tizo']['index']  in ::init() method (must be absolute path)
 - change ::_find() method
 - rewrite the ::level_load() method
 - new static ::is_absolute_path() method
 - small change in ::_log() method
 - source code comment modifications