Merge pull request hbldh#1257 from hbldh/release/0.20.0

Release/v0.20.0

backends/winrt/scanner: wait for scan response for first callback

To make WinRT more like other platforms, we wait for a scan response
if it is expected before issuing the first advertisement callback.
This way, the convenience methods like `find_by_address` will include
the full advertising data similar to other platforms.