Add support for hamlib rig control

[xylo04]

At a minimum, be able to read radio parameters like frequency and mode.

[xylo04]

I have the https://github.com/k0swe/kel-agent/tree/gohamlib branch which integrates https://github.com/dh1tw/goHamlib/. The integration was pretty smooth and is accomplishing the functionality I wanted. However, it creates a dynamically linked dependency on hamlib, requiring the user to already have it installed on their system whether they want to use hamlib or not.

I'd rather decouple the system by integrating with the rigctld TCP protocol. That means a bit of work either finding or creating a replacement, but I think it will be worth it.

[xylo04]

The https://github.com/k0swe/kel-agent/tree/gohamlib branch has been languishing too long. I'm definitely considering the TCP route again.

[xylo04]

https://github.com/k0swe/rigctld-go exposes a couple of useful methods now.