Add support for metrics for Squid log files

[alfh]

I want to use naarad to analyze log files for Apache Traffic Server. It generates files on the Squid log format, so it is really parsing of squid log files.

Is this something that would fit into naarad ?

I've made a working solution at : https://github.com/alfh/naarad/tree/feature_ats_squid_log_support
But I would welcome comments on how to best implement this, and if it is something you see going into naarad.
My working solution is working, but it is more "copy and paste" than I like, based on the Jmeter code.