Implemented Search API

Please cherry pick -my- last commit.
It based branch, user-endpoints which I found `go fmt` and `go test` pass.

In middle of the work, I noticed the search api is legacy which remain there
to meet compatibility with API v2. So, can't encourage people to use it.

But, anyway, hope it helps to more people to involve complete the gothub. :)

Thanks,
Homin Lee.