lib: add standard derivation computation to counter

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
model_utils: better class hierarchy exploration

Now the mainmodule is taken into account to explore the mclass hierarchy
Also, the user can specify a min_visibility to filter things

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
metrics: better design for mclass metrics

MClassMetric is now an interface that is implemented by MClassIntMetric
This allows further developments with MClassFloatMetric

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
metrics: introduce Mendel analysis

This analysis can be used to extract interesting classes from a class hierarchy

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
tests: update tests for nitmetrics

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>