Remove the computations_of trait.
Add argument_pack_as_feature_set.
Regroup feature sets under feature_sets/.
Remove the construction requirement from the FeatureSet concept.
Refactor the feature sets.
Initialize computations from a FeatureSet instead of an ArgumentPack.
Remove the computations typedef from default_.
Reimplement default_ such that computations are initialized properly.
Add the empty feature set.
Rename factories/ to computations/.