Nested param

I implemented this because this param is necessary when you have different Facets types ( nested and string for example) and works fine to me!

How to use:
        $facetcolor = Sherlock::facetBuilder()->Terms()
                    ->fields("options.colors")
                    ->nested("options")
                    ->facetname("Colors");

The Output:
        "Color": {
            "terms":{
                "field":"options.color"
            },
                "nested": "options"
        }
Merge pull request #55 from andersonbento/patch-4

Nested param for facets