Add more metrics

[yangtcai]

Currently, The mAP has been chosen as the metric, however, In the recent training result, I found the value of mAP is always 0, I think it is good to add more metrics, such as precision, and recall. It can help us figure out why the mAP is always 0.

[williamstark01]

Good idea, go ahead with it! For mAP in particular, it may be worth debugging it line by line and by running experiments with small datasets.