Added support for full text querys with custom projections and sort

I need to perform full text querys (http://docs.mongodb.org/manual/reference/operator/query/text/) in my current project. I was able to make the query but I wasn't able to sort or get the full text index score. So I added a new projection parameter that allows me to specify custom json projections. I also made it possible to pass a json object to the current sort method.

**Example with full text index query using the new projection and sort fields**
```
?projection:{"score":{"$meta":"textScore"}}&query:{"$text":{"$search":"demo"}}&select:title,slug&sort:{"score":{"$meta":"textScore"}}
```

Please let me know if you would prefer any other way of implementing full text search.