update docstring of ProblemDefinition.evaluate()
update docstring of ProblemDefinition.evaluate()

rc/sfepy,BubuLK/sfepy,RexFuzzle/sfepy,lokik/sfepy,BubuLK/sfepy,sfepy/sfepy,rc/sfepy,RexFuzzle/sfepy,vlukes/sfepy,vlukes/sfepy,BubuLK/sfepy,sfepy/sfepy,lokik/sfepy,RexFuzzle/sfepy,rc/sfepy,RexFuzzle/sfepy,sfepy/sfepy,lokik/sfepy,vlukes/sfepy,lokik/sfepy