Closing issue #18

Also fixing bug with division by zero in `MethodResults`.

This will introduce a new method API, so users should update their method signatures before using this patch.
- classSetUp(array $methods)
- setUpMethod($method, $iterationsCount)
- tearDownMethod($method, $iterationsCount)
- setUp($method, $currentIteration, $iterationsCount)
- tearDown($method, $iterationsCount)