Finished implementing MLP support (added roll/unroll)

setup.py

xbob/learn/mlp/backprop.cpp

xbob/learn/mlp/cxx/roll.cpp

xbob/learn/mlp/machine.cpp

xbob/learn/mlp/main.cpp

xbob/learn/mlp/roll.cpp

xbob/learn/mlp/rprop.cpp

xbob/learn/mlp/test_roll.py

xbob/learn/mlp/trainer.cpp

xbob/learn/mlp/utils.h