Added tests to expose bugs in running experiments several times in a
row, and fixed them.

I would create several eventSets before, that were not needed. Now I pass
the FeatureSet, and we use the EvenSetBuilder to make an eventSet based
on the FeatureSet. The EventSetBuilder caches eventSets, so it should
not build unnecessary eventSets. It should create only one for a full
run (they don't change often).

I /think/ this helps with a memory leak, you can garbage collect the
results of an experiment as soon as you have consumed it, instead of
keeping it in memory. I'm not certain that's very important, though,
cause we don't store that many elements...

Not strictly necessary, since we don't use the generated EventSet in
Experiment. But might be useful later.

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 normalize the features by using the existing FeatureRatio, it's just
printed differently.

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.

If you already obtained the cycles, no need to evaluate it again.

I removed the parameters numRuns and counters from the constructor of
PapiRunner, this parameter is passed in the specs instead and as a
parameter of the specific functions that need it.

This is so I can pass a PapiRunner without the number of runs to an
Experiment and run it. Otherwise you might have to check the papiRunner
has the same number of runs than the Experiment...

PapiBenchmarkAnalyzer.RunSpec doesn't take
the number of iterations as a parameter anymore, as that's a parameter
of the runner itself (it was always the same value used anyway).

This type is the type we'll use for storing the results of an
experiment, instead of just a list of maps.

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!

Because we might need to iterate on them (and because the eventSet is
actually a list). We want to make sure the counters are not mixed up.