Performance tests

Need to determine performance drop relatively to basic one by one assignment

``` js
var obj = {};
obj.foo = obj.foo || {};
obj.foo.bar = obj.foo.bar || {};
obj.foo.bar.baz = 'quux';
```

and

``` js
var accessDeep = require('access-deep');

var obj = {};
var accessor = accessDeep(obj);

accessor.foo.bar.baz = 'quux';
```
