Run churn metric as library


Added example configuration changes for churn to the .metrics file

Updated the default tmp directory to keep it under the metric_fu structure.

update tests and code.

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Submitting this PR to start the discussion. Likely needs to be rebased and possibly need some additional test coverage. Please take a look and let me know your thoughts. It has been awhile since I have been in the metric_fu codebase so it will take a bit for me to get my feet wet again ;)