Creating and setting up log files
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Highlights:
- Added a text file to log user logins, with timestamp and user id
- Output the log data in logfile.php

Files:
- modified:   includes/functions.php
- new file:   logs/log.txt
- modified:   public/admin/index.php
- new file:   public/admin/logfile.php
- modified:   public/admin/login.php