Synchronise with USB version + move adc sampling into idle function.
Follow usitwislave with moving buffer size to global namespace.
Fill reply buffer only when it's completely done to
avoid corrupted responses when interrupted during
filling.
Don't busy wait for ADC completion, return and check if ADC is
ready during next idle wait call.
Revert "Fill reply buffer only when it's completely done to"

This reverts commit 2726a898a365d38e409ab94c96dc34ad67dc5e13.

Reason: this is not the cause of the problem.
Follow usitwislave to send 0x00 instead of 0xfe when
send buffer is empty.
Cosmetics.
Rev 6.1.3: add calibrated temperature sensors.
Remove corrupted usitwislave.
Re-add usitwislave.
Get new usitwislave version.