Ellipse symmetry

Fixed the #1153 and added several tests for ellipse.
You mean something like this?

```Python
y -= cy
y /= ry
y **= 2
x -= cx
x /= rx
x **=2
y += x
return y < 1
```

I think this will harm readability a lot, so I'd rather leave it in the current form, if you don't mind.