adding audit-series module

[kayozaki]

Adding module which keep track of an in-memory counter, which'll expire over time.

The main usage I'm looking at is to be able to track failures against an external resource.
For example, if RBL calls are timing out i'd want to be able to count the failures and fail-open for a set duration.
Later try again once the failure state expires.
I can call redis to maintain the counter, but redis itself can also go down, thus prefer something quick, local and light.