Find Average Recall and Precision.

[AtriSaxena]

As many people looking to find the Average Recall and Precision like in issue #352 It's better we should add this in evaluation code.

[decoli]

Maybe my understanding is wrong, but I think it should be like this:

    ...
    recs = []
    precs = []
    ...
        ...
        recs += [rec] 
        precs += [prec]
        ...
    ...
    print('Average Recall = {:.4f}'.format(np.mean(recs)))
    print('Average Precision = {:.4f}'.format(np.mean(precs)))
    ...

What do you think?

[AtriSaxena]

Yes. I also did the same changes.