The evaluation metric "Area Under Curve" (AUC) is missing

Created by: tiagofrepereira2012

Issue copied from here: https://github.com/idiap/bob/issues/181

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One well-known evaluation metric for binary classification problems is the Area Under (ROC) Curve: http://en.wikipedia.org/wiki/Receiver_operating_characteristic#Area_under_the_curve

It would be nice to have an implementation of it in bob.measure.