SciKit-Learn Laboratory (SKLL) 0.26.0

Added AdaBoost and KNeighbors classifiers and regressors (finally closing #7). Added support for kernel approximation samplers. (Thanks @nineil) All linear models are now supported by print_model_weights (issue #119). Added f1_score_weighted metric so that weighted F1 will be calculated even for binary classification tasks. Modified f1_score_micro and f1_score_macro to also always return average for binary classification tasks (instead of previous behavior where only performance on positive class was returned)