Automatically impl interface fields

[Zaba505]

If an object implements an interface the user shouldn't have to explicitly add the interface fields to the object. Currently, the implementation mandates this:

interface Iterator {
  next: String
}

type Sentence implements Iterator {
  # next field must be specified
  next: String

  # Now Sentence specific fields
  verbs: [String]
}

The desired usage would look like this:

interface Iterator {
  next: String
}

type Sentence implements Iterator {
  # next field is implied
  # Thus, you can just have sentence specific fields
  verbs: [String]
}