Improve information in CrcFailure

[tobyweston]

When CrcFailures are output, they don't show anything interesting.

Change

case class CrcFailure() extends Error(...")

to

case class CrcFailure(scratchPad: String) extends Error("...")

Then ensure when it's output in the log, it displays the scratchpad.

Also investigate why the stream message isn't displayed. From a recent log:

Fri 19-Jan-2018 09:09:24.835 [temperature-reading-thread-1] ERROR CrcFailure()