Introduce negative learning in Centroid
Fix training with negative learning rate
Minor edits
Set SVQ to use centroid untraining
Data normalization and advanced learning rate(s) in Centroid
Multiple training pass option in Test
Making untraining optional
More flexible SVQ.train() to accept training method
Untraining on least similar centroid (+ minors)
Merge branch 'feature/unlearning' into develop
Merge branch 'release/0.5'
Merge tag '0.5' into develop

Negative learning helps sparse representation