ExtIO wrapper for librtlsdr.
- Original code from josemariaaraujo/ExtIO_RTL
- 03-2020: Fix line endings in files, remove unneeded code and files.
- 12-2020: Fix mem leak, fix UB, add U8 format, add Mingw-w64 Makefiles.
- 11-2021: Add Bias Tee option, add branch auto switch.