lib: fix Counter::clear

Now the sum is also set to 0 when call to clear

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
metrics: clear metrics set between each group analysis

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
model_utils: add attributes count (local + inherited) in MClass
model_utils: add MAttribute::is_nullable

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
metrics: compute number of properties and number of attributes in mclasses_metrics

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
metrics: count nullable attributes

Signed-off-by: Alexandre Terrasa <alexandre@moz-code.org>
metrics: display sums in to_console

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

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

Add metrics about nullables usage in nit_metrics.

Also fix some bugs in metrics collect

Pull-Request: #420
Reviewed-by: Jean Privat <jean@pryen.org>