_.unzip as the inverse of _.zip

[almost]

Based on #1016. I modified @fogus's code to allow tuples of any size, not just pairs.

This function would be very useful I think, I'd love to see it in underscore!

[almost]

I'll show some comparisons between the output of my version (shown here as almostUnzip) and @fogus's version (show here as fogusUnzip)

// Pairs (output is the same)
var zippedArray = [['moe',30],['larry',40],['curly',50]];
console.log(fogusUnzip(zippedArray));
// [['moe','larry','curly'],[30,40,50]]
console.log(almostUnzip(zippedArray));
// [['moe','larry','curly'],[30,40,50]]

// Triples
var zippedArray = [['moe',30, 'stooge 1'],['larry',40, 'stooge 2'],['curly',50, 'stooge 3']];
console.log(fogusUnzip(zippedArray));
// [['moe','larry','curly'],[30,40,50]]
console.log(almostUnzip(zippedArray));
// [['moe','larry','curly'],[30,40,50], ['stooge 1', 'stooge 2', 'stooge 3']]

// 1-tuples
var zippedArray = [['moe'],['larry'],['curly']];
console.log(fogusUnzip(zippedArray));
// [['moe','larry','curly'],[undefined,undefined,undefined]]
console.log(almostUnzip(zippedArray));
// [['moe','larry','curly']]

// 0-tuples (can I call them that? :p)
var zippedArray = [[],[],[]];
console.log(fogusUnzip(zippedArray));
// [[undefined,undefined,undefined],[undefined,undefined,undefined]]
console.log(almostUnzip(zippedArray));
// []

// Empty array
var zippedArray = [];
console.log(fogusUnzip(zippedArray));
// [[],[]]
console.log(almostUnzip(zippedArray));
// []

The only one I'm not sure is better is the emtpy array case, but I still don't think special casing pairs is the right way to go.