LibAudio: Add a FLAC encoder

This encoder can handle all integer formats and sample rates, though
only two channels well. It uses fixed LPC and performs a
close-to-optimal parameter search on the LPC order and residual Rice
parameter, leading to decent compression already.

Userland/Libraries/LibAudio/CMakeLists.txt

@@ -5,6 +5,7 @@ set(SOURCES
     RIFFTypes.cpp
     WavLoader.cpp
     FlacLoader.cpp
+    FlacWriter.cpp
     WavWriter.cpp
     Metadata.cpp
     MP3Loader.cpp