SITE_ROOT, Sessions, Cleanup, extending class

- Created initialize folder and determined the site root and library
root. Then later added a function to pull in other files including
header and footer
- Created login page using a session class. This bug caused me a lot of
grief because I did not add user_id to the session array:
"$_SESSION['user_id'] = $user->id". This also reminded me how to access
an object array item
- Extended the User class by adding a new class DatabaseObject. However,
this was not doable in PHP < 5.3. The problem was static variables and
methods. You cant use self:: because it gets the self object so instead
you can use "static" in place of "self" and  get_called_class() when
instantiating an object in a static function