consider replacing "->" sigil with a word that can be read

When considering #52, I realized that `->` is unnecessarily difficult to pronounce. It bothers me because it obviously wants to be "→" but isn't because of limitations on keyboards rather than comprehensibility. Bagel Fuhmpt could of course format this as an arrow, which would be an improvement, but better yet, I think, would be to change

```
def translate(self, dx: Int, dy: Int, dz: Int) -> Point:
return Point(self.x + dx, self.y + dy, self.z + dz)
```

to

```
def translate(self, dx: Int, dy: Int, dz: Int) returns Point:
return Point(self.x + dx, self.y + dy, self.z + dz)
```

since that is how I would pronounce the sigil; what you are saying about the signature is that it returns `Point`, so... why not just spell that out with a word?