Add a number of numerical features in the client.

    Inputs: - host_name: A string containing the address of the machine where the PServer instance is hosted.
            - client_name: The PServer client name.
            - client_pass: The PServer client's password.
            - feature_names: A python list of feature names.

def add_features(host_name, client_name, client_pass, feature_names):
    """
    Add a number of numerical features in the client.

    Inputs: - host_name: A string containing the address of the machine where the PServer instance is hosted.
            - client_name: The PServer client name.
            - client_pass: The PServer client's password.
            - feature_names: A python list of feature names.
    """
    init_feats = ("&".join(["%s=0"]*len(feature_names))) % tuple(feature_names)
    features_req = construct_request("pers",
                                     client_name,
                                     client_pass,
                                     "addftr",
                                     init_feats)
    send_request(host_name,
                 features_req)