Fixed empty results caching properly

[Moru]

• Empty cache-file is properly recognized by separating cache data and cache status in the return data internally. No more calling the database for empty results.
• Deeper directory structure if needed (property/file.cache) or (property/method/file.cache)
• Logs more errors

[shiraziismailov]

Hello. Thank you for this plugin. I want to delete all cache of all model`s methods. (For example: $this->cache->delete_model_cache("example_model"); )