added an optional log system to track actions & session loss
create the long-term session directory if not exists (used in example)
moved Gearge Argyros's secure_random_bytes function to the main file (the library now depends only on one file)
renamed main file from .class.php to .lib.php because it doesn't only contain 1 class: 2 classes and 1 function
moved long-term related abstract methods to an interface and call them only if needed
moved example files to a subdirectory
added a version number to the code (currently: v3)
updated READM with up-to-date basic and advanced examples