Release v0.1.1

• plot_learning_curve method of module weka.plot.classifiers now accepts a list of test sets;
  * is index of test set in label template string
• added missing_value() methods to weka.core.dataset module and Instance class
• output variable y for convenience method create_instances_from_lists in module
  weka.core.dataset is now optional
• added convenience method create_instances_from_matrices to weka.core.dataset module to easily create
  an Instances object from numpy matrices (x and y)