audio_core: Add initial code for keeping track of audout state.

src/audio_core/CMakeLists.txt

@@ -0,0 +1,11 @@
+add_library(audio_core STATIC
+    audio_out.cpp
+    audio_out.h
+    buffer.h
+    stream.cpp
+    stream.h
+)
+
+create_target_directory_groups(audio_core)
+
+target_link_libraries(audio_core PUBLIC common core)