Logging for audit and debugging

[preaction]

We need to log throughout Yertl. We need to be able to set the log level from the commands. We need to be able to set the default log level through an environment variable.

We need to be able to ship the logs to a collection point. Yertl itself can handle that, exposing itself as a TCP or UDP socket [ymsg] and parsing the input [ygrok], but we need to know where and how to ship it. We probably need to use a log system that knows how to do that.

Log4perl is my first choice, but it's a bit heavy. Log::Any? Log::Dispatch?