aggregated_value method.

Now using singleton method for descendant_results instance.
Using descriptive_statistics to calculate aggregated_values.

signed-off-by: Alessandro Palmeira <alessandro.palmeira@gmail.com>
signed-off-by: Renan Fichberg <rfichberg@gmail.com>
Unused factories for now.

signed-off-by: Alessandro Palmeira <alessandro.palmeira@gmail.com>
signed-off-by: Renan Fichberg <rfichberg@gmail.com>
Metric result factory and some unit tests.

signed-off-by: Alessandro Palmeira <alessandro.palmeira@gmail.com>
signed-off-by: Renen Fichberg <rfichberg@gmail.com>