No need to manually call "accept" on the features, that's kinda ugly

Instead of changing how features are interpreted depending of whether
they work or not, each feature can check itself if it is supported.

We then have a function which builds a new FeatureSet from an existing
one, filtering out the features that aren't supported.

I also added a method that only returns the features that were mentioned
in the FeatureSet in the map of the results.

We don't need to supply a list, the FeatureSet IS a List

Makes the code much cleaner.

We just de-activate the counters that are not avaiable.

Had already disabled it before...

We might want the CostFeature to have the feature we aggregate, but
I used to print "cyclesInsertions", so it makes more sense to me to
constrain it to cycles.

The PAPICounter class checks that the counter works on the current
machine everytime create one. That way, we don't need the list.

This can replace the PapiRunner family of classes.
It just gathers all your features nicely, in a lost less code!

Added some tests too!

We move this to the "papicounters" package, since it uses PAPI.

Takes a specification of features and builds the PAPI eventSet you'd
need to use it.