Bump version to 0.5
Some learning tries.

Unfortunately, we can't compile this with the feature vector sizes we need because of https://github.com/mikeizbicki/HLearn/issues/13.
Implement my own Bayes (not tested)
Learning: Implement safe training/classification
Use FeatureIndex type synonym
Learning: Remove unnecessary Enum label constraints
Learning: Actually implement Bayes correctly (forgot grouping product)
Learning: Add TODO
Learning: Add single label result functions
Learning: Add TODO
Learning: Change error to actuall error
Learning: Don't forget prior (label probability)
Learning: Normalize probabilities
Learning: Add comment
Learning: Filter bad features.

That means: those that introduce 0 variance -> all probabilities 0.
FFT: Remove some old code