how to get the window pos and size?
I have a ``Window`` and can set its ``width`` and ``height``. But when I try to get is position or size, e.g., ``let x = mainwindow.x`` I get an error:
```
config.nim(65, 24) Error: undeclared field: 'x' for type nigui.Window [declared in /home/mark/.nimble/pkgs/nigui-0.2.2/nigui.nim(215, 3)] 
```
What puzzles me is that ``x`` does appear to be a public field.
I'd like to be able to get/set the size and pos so that I can load/save them for the user.