[sphinx] Fixing issues

bob/learn/tensorflow/datashuffler/OnlineSampling.py

bob/learn/tensorflow/network/SequenceNetwork.py

bob/learn/tensorflow/network/__init__.py

bob/learn/tensorflow/test/test_cnn_load.py

bob/learn/tensorflow/test/test_cnn_scratch.py

bob/learn/tensorflow/trainers/SiameseTrainer.py

bob/learn/tensorflow/trainers/Trainer.py

bob/learn/tensorflow/trainers/TripletTrainer.py

doc/nitpick-exceptions.txt

doc/py_api.rst

doc/user_guide.rst