Access to index in "reduce" operation

[youmustfight]

Loving the library so far! One thing that I'm juggling is doing an array operation that references the index. To avoid messing with the api of the map op, I was wondering if we could extend what's accessible in a reduce to include an "index" selector. I see right now it's just "current" and "accumulator"

json-logic-js/logic.js

Line 307 in 045a7fd

{current: current, accumulator: accumulator}