- fixed both SQL files
- fixed `list_pms()`
- fixed `delete_pm()`
- updated CHANGELOG
- added abilty to send `system` PM's for `send_pm()` & `send_pms()`
- changed `name` to `username` in aauth_users table
- changed `name` to `username` in all user related functions
- changed `$name` to `$username` in `create_user()` & `update_user()`
- added `user_exist_by_username()`
- changed `user_exist_by_name()` to an alias of `user_exist_by_username()`