More reduce/map friends

[fasterthanlime]

We only have reduce, and only on Vectors at the time of this writing, but there's a lot more that's in Clojure that we could use, map, map-indexed, reduce-kv, lots of stuff.

See http://clojuredocs.org/clojure.core.

Oh also the for form.

[fasterthanlime]

Lil check list:

• [x] map
• [ ] map (multiple colls)
• [ ] map-indexed
• [ ] reduce-kv
• [x] lazy-seq for all of the above (hahaha) See #2

[fasterthanlime]

Will open individual issues where it makes sense, cf. #80