joe/wukongd: wukongd is a search engine working as a standalone service, based on wukong

xinxin 3d75a88c8c change docId to string type		4 lat temu
..
indexer.go	3d75a88c8c change docId to string type	4 lat temu
indexer_test.go	3d75a88c8c change docId to string type	4 lat temu
ranker.go	3d75a88c8c change docId to string type	4 lat temu
ranker_test.go	3d75a88c8c change docId to string type	4 lat temu
test_utils.go	3d75a88c8c change docId to string type	4 lat temu