Fix for connection loss when pausing music with Sonos by @genekellyjr (issue #71)

• fix for pausing music with Sonos causing the Sonos to close the connection. This optionally injects silence at the music source, contributed by by @genekellyjr (see issue #71), with a new "InjectSilence" boolean flag in the config.toml (not exposed in the GUI). For this to work you have to
  • check that swyh-rs uses the same output as your music source in the Windows soundmixer
  • edit your config.toml and change the InjectSilence flag from false to true
• fltk-sys 1.3.14 builds again on Windows with MSVC, so we no longer need to use the fltk-bundled feature

Windows release and debug binaries, and setup in assets.

Linux release binary in assets (compiled on Ubuntu 22.04.1 LTS).
A universal Linux musl binary is currently not possible because the alsa-sys crate does not support static linking.