Method to replace Magento's own product alerts with an event-based system.

The event system has better functionality and reporting, and is more manageable. It works off an observer that fires off of product price and stock attribute changes. The observer notifies customers who have signed up to receive alerts, immediately. The system also ties into user wishlists.

{{catalog_product_attribute_update_before}} event triggers whenever product attributes change.

There are three types of alerts: Back In Stock, Low Stock (2 or less qty), Price Change (any change to lower than current special_price)