permtuate( arr, n, callback )
Generates permutations (no repetition) from an array. Returns an array of arrays, each inner array being a permutation of arr
arr - required array of anything, or string
n - optional number of choices out of set arr, defaults to arr.length
callback - optional, defaults to:
function(err, result){ if (err) return log(err); return log(result); };
combinate( arr, n, callback ) Same as permutate, but returns all possible combination, duplicate elements in arr are treated as unique