Initial digirig support build v1.1

This is a build of a slightly updated version of my original Digirig support branch, containing a fix for the issue that @penguin359 described here:

ge0rg#382 (comment)

Initial digirig support build

This is the version of the Digrig code that I submitted a PR for here:

ge0rg#382

It's almost identical to the previous test release. Just posting it to be thorough.

Test Release 2

Quite a bit of code cleanup, as well as a POC implementation for syncing the RTS signal to audio playback of the packet.

Test build for PTT via RTS

This is a testing release. I believe PTT via RTS is working, but I haven't been able to do thorough testing yet, due to problems with my radios. Uploading so that others can give it a try. Use at your own risk!