* add caller and stack Valuer functions
* Add WithPrefix and WithSuffix similar to what go-kit offers
* replace New with just `with`. Remove filter wrapper because the first argument of the context argument is not logger but additional context.
* update Xorm logger to use custom depth to display the datastore code instead of xorm
* Update API to call the scheduler to remove\update an alert rule. When a rule is updated by a user, the scheduler will remove the currently firing alert instances and clean up the state cache.
* Update evaluation loop in the scheduler to support one more channel that is used to communicate updates to it.
* Improved rule deletion from the internal registry.
* Move alert rule version from the internal registry (structure alertRuleInfo) closer rule evaluation loop (to evaluation task structure), which will make the registry values immutable.
* Extract notification code to a separate function to reuse in update flow.
* change registry.delete to return deleted struct
* use pointer to alertRuleInfo instead copying.
* do not access evaluation channel when routine is stopped
* remove stopCh and use context cancellation
* do not return ctx.Err when channel is cancelled because it cancels all other routines
* make alertRuleInfo fields and functions package private
Yuriy Tseretyan
