Optionally create default InMemory cache if ICache not found

[NoahLerner]

By adding the initializeIfMissing parameter to the CacheAttribute, library users can ensure that they won't encounter 100% cache misses if the configuration is missing or deleted.

Usage

[Cache("missingCacheName", true)]    // creates an `InMemoryCache` with a 1 day sliding expiration
public void MyMethod(){
}