MRG: merge from _tent/clust
BF: support sample dimension
BF+ACK: ensure that neighborhood is properly set even if elements are missing. Thanks to #Daniel Kaiser# for reporting this issue
BF: support the case of single feature and sample dimension
OPT: only check dataset once, not for every split
BF+ACK: fix error message when size of dataset and target matrix is not matched. Thanks to #Liuba Papeo# for reporting this issue