Add running averages as members of RMSProp class

This enables us to use them as monitored values.
Reorder things in SGD.setup, so we call learning_rule.get_updates
before learning_rule.add_monitoring_channels.
Also add a little bit of doc.
PEP8 compliancy
Merge pull request #2 from madisonmay/rmsprop-monitoring

PEP8 compliancy
Merge pull request #1 from lamblin/madisonmay-master

Add running averages as members of RMSProp class