Add callEach and callMap

They will iterate over a collection using _.each and _.map respectivly
calling a function on each item.

Use case
---
There are a lot of times I want to invoke a function on each object in a collection, below are some use cases in code.

```javascript
function Missile() {}
Missile.prototype.fire = function() {
  console.log('The missile has been fired');
}

var missiles = [new Missile(), new Missile()];
// Prints 'The missile has been fire' twice
_.callEach(missiles, 'fire');
```

```javascript
function Person(name) {
  this.name = name;
}
Missile.prototype.greeting = function() {
  return 'Hello, ' + this.name;
}

var people = [new Person('Jane'), new Missile('John')];
_.mapEach(people, 'greeting') // ['Hello, Jane', 'Hello, John']
```

Naming
---
I tried finding a name similar to `pluck` which I feel this is a close to, but I came up short.