wdte: Add `rev` and `method` (#198) * wdte: Remove `Func` from `Assigner`. * res/grammar: Add `rev` and `method` funcmods. * scanner: Add `rev` and `method` keywords. * wdte: Refactor function creation into a shared function. * wdte: Implement `rev` and `method`. * wdte: Don't use 'fmt.Sprint()' to write to a `strings.Builder`. Huh. What in the world.