Tasks

## Underbar
* [ ] Implement an `.each` function
- Requires: none

## Underbar
* [ ] Implement a `.reduce` function
- Requires: _.each

## Underbar
* [ ] Implement a `.contains` function
- Requires: _.reduce

## Underbar
* [ ] Implement a `.defaults` function
- Requires: _.each

## Underbar
* [ ] Implement a `.once` function
- Requires: just some fancy smancy stuff

## Underbar
* [ ] Implement a `reduceRight` function
  * Do not use any external function calls (even to helpers) within your implementation.
  * `reduceRight` behaves much the same as `_.reduce`, but traverses the target in the opposite direction.
  * Remember that `_.reduce` behaves differently if you do not provide it a `memo` argument:
    * If no `memo` is passed, the last element is used and is never passed to the iterator. 
  * Note: your function only needs to work correctly on arrays.
- Requires: whatever you want