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.
I've also just set up Travis-CI for my fork of pylearn2, so I can also report back with test results once that completes.