This adds support for newly defined objects immediately implementing a
trait. This means that instead of having to write this:

    import std::conversion::ToString

    object Person {}

    impl ToString for Person {
      def to_string -> String {
        '...'
      }
    }

You can instead write the following

    import std::conversion::ToString

    object Person impl ToString {
      def to_string -> String {
        '...'
      }
    }