Can't initialize Compare with list of features

[jpweytjens]

When a Compare class is initialized with a list of features, the returned class has no features. This is caused by the following lines in base.py

def __init__(self, features=[], n_jobs=1, indexing_type='label',
                 **kwargs):

    self.features = []
    self.add(features)

    # public
    if n_jobs == -1:
        self.n_jobs = cpu_count()
    else:
        self.n_jobs = n_jobs

    self.indexing_type = indexing_type  # label of position
    self.features = []

The features are added to self.features, but later removed again. I will write a small PR to fix this issue.