Allow to filter imports by multiple packages.

[omeid]

Hello there,

I would like to be able to find packages that import a specific set of packages.

For example, show all packages that import mgo, Gorilla/mux, and someother/pkg. In other words:

{http://godoc.org/labix.org/v2/mgo?importers} ∩ {http://godoc.org/github.com/gorilla/mux?importers} ∩ {http://godoc.org/path.to/someother/pkg?importers}

Perhaps like so:

http://godoc.org/labix.org/v2/mgo?importers?filter=imports:github.com/gorilla/mux&&path.to/someother/pkg

or however it is convenient.