Define reverse explicitly

http://jsperf.com/r-reverse-e

Couple different options
 - fb5b242d474296abf23fd0e2e1953c10604c3cd6
 - via `map` a91f33bb9c07a0aa424fb9f6541bff0169258ac0
 - Refactor `_slice` c2729bbe21c659d596ab178619bd66a81e2038e3

Feel free to punt this. I just hate `[].reverse`