[Coco] how to get brackets and braces with MAME in "natural" mode

[James Jones]

With help from various folks, to whom many thanks, I can come up on an RPi3
with Ron Klein's "CocoPi3" image and emulate a CoCo 3 with 6309 and run the
6309 beta of NitrOS-9 "Ease of Use", but...

...I've lost the muscle memory I developed decades ago typing on a CoCo 3
keyboard, and for that matter when doing this I'm typing on a generic
PClone keyboard. I don't want to have to keep a poster of the CoCo 3
keyboard up by the RPi.

Supposedly handing mame the option "-natural" turns off that mapping, and
for the most part it works, except that I can't find a way to type any of
{, }, [, or ].  Anyone out there running MAME in "natural" mode who can
type a brace or bracket?

James