Last published flag doesn't work with multiple sensors

[Floppy]

Only one sensor can be published every ten seconds, as opposed to multiple sensors with a maximum rate of once per ten seconds per sensor. Also, if a sensor isn't read in the loop that publishes, that reading is completely lost, so slow sensors are likely to be completely swamped.

[Floppy]

This just needs last_published and last_value to be in a hash for each sensor.