soapy-sdr: updated to 0.8.1

Release 0.8.1 (2021-07-25)
==========================

- cmake: fix use of CMAKE_INSTALL_LIB_DIR when absolute
- windows: Fix compatibility with non-MSVC compilers
- cmake: version policies for subproject compatibility
- docs: fixed spelling mistakes in doxygen comments
- python3: change OUTPUT_NAME in newer versions of cmake
- Types: consistency changes converting strings to bool
- Type.hpp: fixed templated StringToSetting return true
- Range: fixed default constructor not initializing step

Release 0.8.0 (2021-04-25)
==========================

Build:
- Update to CMake 3.0 style and project config generation
- Increase the CMake build requirement to version 3.1.0

API:
- Added API calls for configuring an external reference clock rate
- Constants for boolean setting strings SOAPY_SDR_TRUE/FALSE
- Templated read/writeSetting()/readSensor() for SoapySDR::Device
- Added Templated StringToSetting() and SettingToString() helpers
- Python bindings duck typing for read/writeSetting()/readSensor()
- Changed SoapySDRDevice_setupStream() to return the stream pointer
- Added unloadModules() API call to manually cleanup modules on exit
- Device: added parallel make() function with string arguments
- Added ABI check to Python module

(adam)