macOS support

I tried to use `libvosk.dylib` from [vosk-0.3.45](https://repo1.maven.org/maven2/com/alphacephei/vosk/0.3.45/) and got an error:
```zsh
Building macOS application...
dyld[1236]: Library not loaded: 'libvosk.dylib'
Referenced from: '/Users/mac/projects/flutter/vosk-flutter/example/build/macos/Build/Products/Debug/vosk_flutter_example.app/Contents/MacOS/vosk_flutter_example'
Reason: tried: 'libvosk.dylib' (no such file), '/usr/local/lib/libvosk.dylib' (no such file), '/usr/lib/libvosk.dylib' (no such file), '/Users/mac/projects/flutter/vosk-flutter/example/libvosk.dylib' (no such file), '/usr/local/lib/libvosk.dylib' (no such file), '/usr/lib/libvosk.dylib' (no such file)
```
After [a little investigation](https://developer.apple.com/documentation/xcode/embedding-nonstandard-code-structures-in-a-bundle), I found that `libvosk.dylib` does have a non-rpath reference inside, which is causing the problem:
```zsh
mac@Mac-mini-Mac Libraries % otool -L libvosk.dylib
libvosk.dylib:
libvosk.dylib (compatibility version 0.0.0, current version 0.0.0) # <- this one
/System/Library/Frameworks/Accelerate.framework/Versions/A/Accelerate (compatibility version 1.0.0, current version 4.0.0)
/usr/lib/libc++.1.dylib (compatibility version 1.0.0, current version 1200.3.0)
/usr/lib/libSystem.B.dylib (compatibility version 1.0.0, current version 1311.0.0)
```

But I'm not much in macOS and CMake, so would appreciate any help in compiling the voks-api with RPATH enabled 🙏