added simple wave classes

To assist the input/output of PCM data, we use the fairly straight-forward
WAVE format. These classes simplify the input and output of such data.

app/decoder/waveoutput.h

@@ -0,0 +1,41 @@
+#ifndef WAVEAUDIO_H
+#define WAVEAUDIO_H
+
+#include <QByteArray>
+#include <QFile>
+
+#include "audio/sampleformat.h"
+#include "render/audioparams.h"
+
+class WaveOutput
+{
+public:
+  WaveOutput(const QString& f,
+             const AudioRenderingParams& params);
+
+  ~WaveOutput();
+
+  Q_DISABLE_COPY_MOVE(WaveOutput)
+
+  bool open();
+
+  void write(const QByteArray& bytes);
+  void write(const char* bytes, int length);
+
+  void close();
+
+private:
+  template<typename T>
+  void write_int(QFile* file, T integer);
+
+  void switch_endianness(QByteArray &array);
+
+  QFile file_;
+
+  AudioRenderingParams params_;
+
+  int data_length_;
+
+};
+
+#endif // WAVEAUDIO_H