New OOT module for SDRplay RSP devices

[Franco VENTURI]

I just pushed a new OOT module for SDRplay RSP devices on Github here: https://github.com/fventuri/gr-sdrplay3

A few important notes:

- the module uses SDRplay API V3

- the module builds with the latest version of GNU Radio (3.9 - master branch) - Python bindings use pybind11

- the module supports the following RSP models:

  - RSP1

  - RSP1A

  - RSP2

  - RSPduo (all modes of operation)

  - RSPdx

This is still a work in progress - I only ran a few basic tests with a few of them (RSP2, RSPduo, and RSPdx), and I just checked that it was streaming without crashes or other major problems.

Please feel free to give it a try - let me know if you find any problem (I am pretty sure there are still a few bugs).

Regards,

Franco Venturi - K4VZ