Add options for category search

[souperneon]

@orangejulius let's do this!

[louh]

What is this?

[louh]

(I'm very aggressively closing down / cleaning up issues in this repo, so I'm wondering if this is (a) already solved or doable in some other way, (b) something we kick into a "v2" label, (c) close entirely with no further fanfare.)

[souperneon]

@orangejulius does pelias haave category search now? (sorry I should know this :|)