Add brightness control

[mpember]

A brightness variable make it possible to set a maximum LED brightness.

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[mpember]

I signed it!!

[googlebot]

CLAs look good, thanks!

[mpember]

Is there a preferred method of checking the brightness variable is valid? I considered having it expect an integer between 0-100 and testing the range. From there, it would be divided by 100 and stored in the brightness variable.