Implement RadioGroup::{row,column,for_axis} to allow layout customization

[twitchyliquid64]

Trivial change to allow the user to set the Axis on which Radio's are laid out. Breaking change in that RadioGroup::new is now RadioGroup::column.

Builder methods column(), row(), for_axis() are consistent with the Flex widget.

[jneem]

Thanks for the PR! I'd be inclined to copy the Flex naming for consistency, even if it is a breaking change. (e.g. RadioGroup::column, RadioGroup::row, and RadioGroup::for_axis) What do you think about that?

[twitchyliquid64]

Sure thing! I'll get on it this weekend :)

[twitchyliquid64]

Done! please take a look :)

[jneem]

Looks great, thanks! We'll definitely want a changelog entry too (which I can do today if you don't have time).

(Note that the links in the changelog aren't automatic; they're all defined at the bottom)

[twitchyliquid64]

Done, thanks!

[jneem]

Thanks for your patience! I have to wait for CI to finish, and then I'll merge.