Summary:
Main changes:
1. Move reader creation to Brew in order to be consistent and avoid a wild use of param_init_net
2. Use optimizers for training function, avoid manual optimizer construction
3. Add MLP mode (a default)
4. Fix a bunch of too verbose comments and add a bit of new explanations
Closes https://github.com/caffe2/caffe2/pull/1760
Differential Revision: D6749059
Pulled By: salexspb
fbshipit-source-id: 9dfbbb2d9772a74a0300c2e404a92e791f7cc593