New fields

I added some fields that were alredy defined in grape_doc, but it wasn't consuming the info from the grape inmplementation. This will add field type to the doc, and sample value, which are set while defining params on a grape implementation. For sample value, as suggested by grape main doc, you can use 
```
:documentation => {:example => 'some example'}}
```

 to add a sample value. Also I fixed and updated minor other minor things. I'm currently using this gem, and I might also add in the future, the response example for each endpoint defined on the grape api.