Add producer consumer validation checks

Since #5 we now store the produced and consumes. We now need to ensure that we have a series of checks. These should produce warning and error logs:
* Error: consumeFromStep whould in fact consume a method.
* Warning : If we produce unnecessary keys, this hould be a warnining
* Error : Consuming a key that is not produced earlier

Start by reviewing issue #5 and the code that stores the produced and consumed values. Trace where producer-consumer relationships are evaluated, then determine how warning and error logs are emitted. Done means the three listed checks are covered: invalid consumeFromStep methods and unproduced keys produce errors, while unnecessary produced keys produce warnings.

Written by the indexing model from the issue text.