add audio Seek functionality

src/Audio/SoundInstance.cs

@@ -241,6 +241,8 @@ namespace MoonWorks.Audio
 		public abstract void Play(bool loop);
 		public abstract void Pause();
 		public abstract void Stop(bool immediate);
+		public abstract void Seek(float seconds);
+		public abstract void Seek(uint sampleFrame);
 
 		private void InitDSPSettings(uint srcChannels)
 		{

src/Audio/StaticSoundInstance.cs

@@ -93,6 +93,31 @@ namespace MoonWorks.Audio
 			}
 		}
 
+		private void PerformSeek(uint sampleFrame)
+		{
+			if (State == SoundState.Playing)
+			{
+				FAudio.FAudioSourceVoice_Stop(Handle, 0, 0);
+				FAudio.FAudioSourceVoice_FlushSourceBuffers(Handle);
+			}
+
+			Parent.Handle.PlayBegin = sampleFrame;
+			Play();
+		}
+
+		public override void Seek(float seconds)
+		{
+			uint sampleFrame =
+				(uint) (Parent.SamplesPerSecond * seconds);
+
+			PerformSeek(sampleFrame);
+		}
+
+		public override void Seek(uint sampleFrame)
+		{
+			PerformSeek(sampleFrame);
+		}
+
 		public void Free()
 		{
 			Parent.FreeInstance(this);

src/Audio/StreamingSoundOgg.cs

@@ -62,6 +62,35 @@ namespace MoonWorks.Audio
 			device.AddDynamicSoundInstance(this);
 		}
 
+		private void PerformSeek(uint sampleFrame)
+		{
+			if (State == SoundState.Playing)
+			{
+				FAudio.FAudioSourceVoice_Stop(Handle, 0, 0);
+			}
+
+			FAudio.FAudioSourceVoice_FlushSourceBuffers(Handle);
+			ClearBuffers();
+			FAudio.stb_vorbis_seek(VorbisHandle, sampleFrame);
+			QueueBuffers();
+
+			if (State == SoundState.Playing)
+			{
+				Play();
+			}
+		}
+
+		public override void Seek(float seconds)
+		{
+			uint sampleFrame = (uint) (Info.sample_rate * seconds);
+			PerformSeek(sampleFrame);
+		}
+
+		public override void Seek(uint sampleFrame)
+		{
+			PerformSeek(sampleFrame);
+		}
+
 		protected override void AddBuffer(
 			out float[] buffer,
 			out uint bufferOffset,