M17 support
M17 is a new digital radio protocol for data and voice, made by and for amateur radio operators. More details here. Implementation in SDRangel consists in a pair of Rx and Tx channel plugins. This implements issue #1259
Other changes and fixes
- AIS: NMEA sentences must end with CR/LF. Issue #1333. PR #1342
- Darken ValueDials when disabled. PR #1331
- Map: Fix capitalisation of Radiosonde so settings are found. Fixes #1318. PR #1320
- USRP: Catch all exceptions from set_rx_agc. PR #1315
- GLScope and GLSpectrum removed extraneous call to cleanup method. Fixes #1295
- Update to sdrangel-windows-libraries with UHD 4.2.0. PR #1314