Event Caching - Honor Pragma:no-cache header

There are certain times it might be necessary to bypass the cache at an individual request level. Since the cache key is constructed from the context, it makes sense to handle this clearing from within the `runEvent` method, when a cache response is evaluated.

When the header `Pragma: no-cache` is received ( which is the same header sent by browser dev tools when the "disable cache" option is selected ), the runEvent method should clear the cache for the detected key and run the event fresh ( thus, repopulating the cache )