Issue 39

There may still be some rough edges here. In particular, it feels like `CacheWriter.write(K, V)` needs to be split into insert and update, and return a value. Also, an attempt was made to whip compute/write functions for bulk CRUD methods into shape, to blaze the trail for fixing #110... not super convinced they are correct now though.
Wonder whether it wouldn't be clearer to call this `tryRemoveFromCacheAndDelegateToResilienceStrategy` or something... i.e. a method name that translates what it does clearly. It's private, called from catch blocks, I think it would be clearer if its name reflected the actual concrete intent of it.