More alerts work.

Added alerts clean up in get_alerts() function. This uses ZREMRANGEBYSCORE to clear out alerts older than 4 weeks (K.EXPIRE_4WKS)

Added unit tests to check get_alerts() and ensure it is cleaning. Still more testing required.

Adjusted comment for new timestamp() function.

I have a conversation open in Issue #13 basically my ramblings. This new work addresses some of those issues.