Move template functions to separate file
Add tests for custom template functions
Add logrotate example

Example template that uses a comma-separated value of log files
stored in a container environment variable named "LOG_FILES."  The
value is split on the comma character and then each log file is
listed in the logrotate config file through the hosts file system.

Each container's docker JSON log file is also listed for rotation
to prevent it from growin indefinitely.