Embedded structs are not being serialized.

``` go
type Foo struct {
     Name      string    `jsonapi:"attr,name"`
     CreatedOn time.Time `jsonapi:"attr,createdOn"`
}

type Bar struct {
     Foo    
     ID   string `jsonapi:"primary,bars"`
     Last string `jsonapi:"attr,last"`
}
```

Marshaling Bar struct, ignores embedded fields from Foo (i.e. name, createdOn)
