Bug on the new version (0.0.6) of the firmware
There is a bug (a small type) that prevents the new version to compile if you choose CURRENT_VARIANT_MILL_AMP. So, until the maintainer fix it, you have to make changes by yourself.
The name of the constant defined at line 119 is "CurrentVariant" and not "currentVariant" as originarely shipped with the library sources.
Nice catch - thanks for posting this. I've fixed the issue and pushed latest version to the repository on bitbucket.