Rename some functions to general/better names

- 'get_dunder_key' to 'dunder_key_val'
- 'filter_entries' to 'filter_items'
- 'entry/entries' renamed to more general 'item/items'
Rename test
Add support for compount lookups and refactor

This commit adds support to compound lookup via Q objects (similar to
the Q objects in Django). The filter items code is refactored. Some
tests are added and old ones fixed.
Add support for nested filtering and update tests
Rename the project files to a more general name

Pyharbor --> Lookupy