make caching optional

[bensialih]

Fixes #12
added caching variable to make caching optional. Unit tests added to test this.

Motivation
When adding facts dynamically, I would like to make the same query multiple times.
Making the same query multiple times will only returned the cache results instead of the updated results.

Solution
Add marker to allow caching to be optional to the query function.

Unit tests
create new KnowledgeBase and add new entries to highlight the problem.
create new KnowledgeBase and add new entries and make the same queries with the cache marker set to False.