Problem with "SerialCommandsArguments" Example

I was testing this out on an STM32L0 and I found that my program was freezing before the commands even started. I eventually tracked it down to the `set_led` function having no return value. Adding `return true` to line 99 fixed the problem.
Apologies for not issuing a pull request or submitting a patch as I'm nots sure how to do that.