WIP: Support for Voltronic Axpert P30 protocol inverters (main)

[minfrin]

Adds support for the Voltronic Axpert inverters based on the P30 protocol.

Updated the nutdrv_qx driver to support the optional sending of commands
protected by CRC.

Initial support for query commands. Based on work done in the Voltronic
Sunny driver in https://github.com/nickma82/nut/tree/nutdrv_qx_voltronic-sunny_rebased+command

Still TODO:

Implement commands to write to the inverter.
Remove commented code originating from sunny driver.
Further testing.
Update docs (manpages, acknowledgements, NEWS.adoc...)

[lgtm-com]

This pull request introduces 1 alert when merging 5375524 into 9cb8de6 - view on LGTM.com

new alerts:

• 1 for Comparison of narrow type with wide type in loop condition

[jimklimov]

@minfrin : I marked the PR as draft for now, so it would not burden CI with failing code to build ephemeral merges as master branch marches on. Feel free to un-set draft mode when needed to test fixes to broken builds.

[minfrin]

Thanks for this.

All the parameters being read are working well, and it's doing the job.

Testing the write functions is tricky, as the inverter is powering the machine it was developed on, so options are limited. Lining up a time to do safe testing.

[jimklimov]

Cheers! Wondering if you have any updates on this? :)

[jimklimov]

Resyncing with main NUT code base after v2.8.3 release.

[AppVeyorBot]

❌ Build nut 2.8.3.3052-master failed (commit 840d782003 by @jimklimov)

[jimklimov]

Proposed a NEWS.adoc entry usable in case of immediate merge (as an experimental driver at least, potentially for NUT community to share on further completion).

[jimklimov]

@minfrin : I've updated this PR branch to the extent that I think the code is mergeable "quality-wise": there are changes to news and man pages, the questionable data points and related methods are hidden with #ifdef as "unmapped" items in some other drivers (and whatever concept names did not fit existing NUT standards, were renamed to the experimental.* namespace).

In your original post you've had plans for further work, and named this PR as a "WIP"... do you have any reservations (like this code is only a boilerplate and not really functional with the devices), or can it be merged as it is now and continued in later PRs? Do you see yourself doing that in short term, BTW? :)