Added a new LearningRule object, which computes parameter updates from
gradients. Implemented `Momentum` and `AdaDelta` learning rule.
Added more documentation to LearningRule objects.
Introduced bugs when preparing for pull requests.
Added unit-test for new learning rules.
Moved MomentumAdjustor from sgd.py to learning_rule.py.

MomentumAdjustor will work with both old and new interface of momentum, until
init_momentum is deprecated.
Updated YAML files to use new learning_rule.Momentum interface.
Added parameter to MonitorBased termination criterion, to allow
stopping on a smoothed (running average) monitoring channel.
Added "skip" parameter to Preprocessor, Standardize and
GlobalContrastNormalization
Bug fix to work with latest pylearn2 training scripts.
Added contractive CAE cost object.
Store `nvis` as attribute of AutoEncoder objects.
Merge branch 'master' of github.com:gdesjardins/pylearn2_bio