Resolve "Implement first version of a `RuleHandler`"

The RuleHandler should deal with a set of rules. In the future, this is the class that should communicate with a rule database & with inserting/updating/removing features in the databases. However, in the first version it should deal the basic functions, such as registering / deregistering rules and evaluating a set of rules.

Closes #3 (closed)

\approve @ds

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