Adjusters will be used to modify a list of Features. This could either be:

 - to modify the overall set (eg to target a time)
 - to modify individual Features

The most important Adjuster will be one that targets an overall time, eg:

"modify this list of Features such that their times add up to 1 minute (either ±
a % or a hard limit)"

@see: feature_extractors.py::FeatureExtractor