Add delete_all/2 and count_all/2 functions to the Cache API

[cabol]

Add delete_all/2 and count_all/2 as part of the queryable behaviour.

• delete_all/2: Deletes all entries matching the given query. If query is nil, then all entries in the cache are deleted.
• count_all/2: Counts all entries in cache matching the given query. If the query is nil (the default), then the total number of cached entries is returned.

These new callbacks should replace size/0 and flush/0. For example, Cache.size() == Cache.count_all() and Cache.flush() == Cache.deletee_all().