Fall back to discontinous reads of discrete outputs

[alexrudd2]

I'm not sure of my approach here, hence the separate branch.

This more or less works, although in my case trying to read ~180 tags sequentially takes >1 s and so the regular controller read() loop timesout unless I slow it down. It also generates a lot of logging if you have many broken writes! Would it be smarter to stop polling addresses with some sort of blacklist if they return an exception?

Also, this error was introduced but doesn't appear to affect anything?

ERROR:pymodbus.client.asynchronous.asyncio:Factory protocol connect callback called while connected.

[alexrudd2]

Interesting, apparently we can now do drafts for public repos, but not private?!