Enable package search

[dogweather]

I came to Stackage to search for split, as it's referred to in a .cabal file. But I get a list of results which don't seem to be ordered; a list of functions named split from various packages:

Search will return the module only if I already know it's namespaced module name:

And now, the search engine results seem to be ordered for relevance.

Summary

1. Facilitate package name searches either by ranking them high in relevance or displaying them parallel to function searches.
2. Use package name match as a component of relevance generally.

I'm happy to help implement these.

[snoyberg]

The search functionality is just an API search, but I don't see a problem with checking if the searched name matches a package name and providing that as the first search result. If you'd like to take a stab at a PR for that, I'd be happy to review.