Improvements:
PR 18 : Avoid doing the transformation of the input data for every step of the pipeline, only doing it once.
PR 19 : Optimization of check_pipeline_order
PR 20 : Precalculate stopwords
PR 21 : Optimization of regroup_data_series
Bugfixes :
PR 22 : The local version was suffixed "-local". Now it will be "+local"