Make Python Script Executable
Rename user_agent

The variable user_agent isn't really being treated as a constant, so
don't use all uppercase.
Add Way to Change Log Level Output

Put in verbose and debug flag support to allow the user running the
script to change the level of log output on run.
Backup Retention Cleanup

Support a way to retain only a specified number of list backup files.
Add function to execute the cleanup and a config setting to allow the
user to define the number of backups to keep.
Cleanup Download Log Message

Make the info log message when downloading the list a little nicer.