[WIP] Implementing Averaged SGD

Working on implementing averaged SGD for both classifier and regressor for #543
What about the case ```X = [1, 0, 1]``` and ```y = [1, 1, 1]```. The weights and average_weights should both be 1 at the end. Wouldn't adding ```T - t``` yield an average_weight vector of ```4/3```?
```
T = 3
i = 0  w = 1  aw = 3 
i = 1  w = 1  aw = 3 
i = 2  w = 1  aw = 4
aw /= T
```