Autosized buttons
Is there any way to make a button that sizes itself to its text? This seems like it should be really simple, but I can't seem to figure it out. As far as I can tell, the examples all just manually set the size of the button. The best I've been able to figure out is something like this, which is really inelegant:

```nim
- Button:
  width == systemFont().sizeOfString("hello").width + 10
  height == systemFont().sizeOfString("hello").height + 10

  title: "hello"
```