Depth search for object

Provide a depth search in object.

```javascript
var obj = {foo: "bar", depth: {object: {really: "depth"}}};

var res = _.depth(obj, "depth", "object");
// res = {really: "depth"}

var second = _.depth(obj, "foo");
// second = "bar"

var thrid = _.depth(obj, "bin");
// third = false

```

See ya