add the retrieval model based on jaccard and euclidean distance

[Cheng-Su]

I implemented two recall model based on jaccard distance, euclidean distance respectively. The model effect as follows:	model	Precision@20	Recall@20	MAP@20
jaccard	0.00429635	0.08592715	0.02708586
euclidean	0.00019867	0.00397350	0.00228660