Add support to encode flac

Update ExtraConfig's default value

src/utils/lossless_audio.rs

@@ -0,0 +1,19 @@
+//! Lossless audio utilities.
+use super::flac::*;
+use super::pcm::*;
+use crate::types::*;
+use anyhow::Result;
+use std::io::{Read, Seek, Write};
+
+pub fn write_audio<W: Write + Seek, R: Read>(
+    header: &PcmFormat,
+    reader: R,
+    writer: W,
+    config: &ExtraConfig,
+) -> Result<()> {
+    match config.lossless_audio_fmt {
+        LosslessAudioFormat::Wav => write_pcm(header, reader, writer)?,
+        LosslessAudioFormat::Flac => write_flac(header, reader, writer, config)?,
+    }
+    Ok(())
+}