Add support for Colemak keyboard layout

[GlenHertz]

I bought some OnlyKeys but Colemak keyboard layout isn't supported so it is a real pain to use since I remap the USB keys at the registry level in Linux and Windows. Is there any way to get Colemak keyboard support (based off standard US keyboard)? Otherwise I have to remap the keys ahead of time but then when I use it with my cell phone where the keys are not mapped it will not work. Ideally there would be an easy way to switch keyboard layouts between Colemak and regular US QWERTY.

[onlykey]

We have been a bit busy with other features but we do want to support additional keyboard layouts. Would you be able to do a pull request for this? Here is an example of a pull request to add a keyboard layout - #90