Need to provide a minimal cache API that includes at least the following methods:
- reading a value for a given key
- writing a new value for a given key
- remove a value for a given key
- method that determines if the cache contains an entry for the specified key.
- a way to iterate all key/value pairs
- cache/table size (this method is questionable)
Additionally, it can be considered adding a way to execute the user's code for the specified key - something like Cache#invoke()